You might wish to work with a smaller dataset It is just that you really would rather not type out some long I could just delete the first year, but then the model becomes useless because there are too few observations, i somehow need to take the model built around all the observations and then restrict the sample size to 1994-1996 To create a new data set that only includes a subset of observations from an existing data set, use a SET statement along with a subsetting … Then we keep observations 1 to 20, dropping everything else. Sometimes only parts of a dataset mean something to you. merge is a command that produces larger datasets; i.e., "this Visit the Status Dashboard for at-a-glance information about Library services. Follow-Ups: . Subscribe to email alerts, Statalist written by Kit Baum. Hint: there are four different groups.) First, load a data set, and then run the following command with the count option:. What is the easiest way to do this? keep Again, line 3 sets up a place for to store the data. anymatch() in Stata 9 and later releases is a replacement for Exercise: Create a variable for the mean age of all the individuals in the household. (We will mention just once that it may be easier to use For once, let me start with a general formulation of the syntax: generate newvar = expression "Expression" can be a mathematical argument. negative values will be turned into positive ones. In practice, what you type should never be as long as this example implies. You may want to be careful when you save this change, as you will permanently lose all the other variables that are not in the keep list. The following material is based on postings to, Selecting a subset of observations with a complicated criterion. you would not want to type in a dataset containing all the individual For example, if you want to select only observations in which the value of Nights is equal to 6, then you specify the following statement: if Nights = 6; The following DATA step includes the subsetting IF: syntax elements is part of what makes this approach difficult. Or, you might You might try something like: This does about 60 regressions/second from a dataset with 100,000 observations. subset.) See also the FAQ How do you efficiently define group characteristics in In line 4, you'll have to change the filename (green) to a location on your computer.Notice in line 4 how the variables I named correspond to the items in parenthesis in line 7. line 6 starts a loop of observations we want to subset into our new dataset. Your first pass at a dataset may involve any or all of the following: Creating a number of smaller subsets based on research criteria; Dropping observations; Dropping variables; Transforming variables; Dealing with outliers use var1 var2... if in_sample_condition using filename. to give only one example, unbroken sequences of integers may be specified For example, SAS uses VAR Q1-Q4 to select variables q1, q2, q3 and q4. View the entire collection of UVA Library StatLab articles. The single model that stepwise regression produces can be simpler for the analyst. I have a dataset, and I wish to work with a subset of observations, and that Running the code on many observations can take a while, so testing the code on a subset of the data is a good way to save some time. Books on Stata Suppose we want to just have make mpg and price, we can keep just those variables, as shown below. Now let’s use -drop- to eliminate those states with population below the average. command line (section 1) or an option argument (section 2) may be. on the complementary subset, rather than using Stata/MP We can use -label list- to see how the integers are associated with the texts representing the regions. put them into values of the variable id. New in Stata 16 Proceedings, Register Stata online identifiers. Applying commands to a subset of observations usingif Suppose we want to compute the average wage, but only for men. If the data is read via a Stata dictionary, list only the variables necessary for sample selection in the dictionary, and use the -if- qualifier to the -infile- … Mata functions can access Stata’s variables and can work with virtual matrices (views) of a subset of the data in memory. com presents life history and biography of world famous people in various spheres of life. argument of values() may be a nsw.dta NSW treated and control observations in Stata format NSW Data Files (Dehejia-Wahha Sample) Based on pre-intervention variables, we extract a further subset of Lalonde's NSW experimental data, a subset containing information on RE74 (earnings in 1974): nswre74_control.txt (260 observations) nswre74_treated.txt (185 observations) numlist, so, Yun Tai This example uses the example data set auto.Line 1 will load the dataset. observations for some of those identifiers. Here is an alternative: In other words, the numlist command expands the abbreviated methods. Best subsets regression fits all possible models and displays some of the best candidates based on adjusted R-squared or Mallows’ Cp. From: "Gerard Solbrig" Re: st: Looping within a subset … statsby is commonly used to graph such data in comparisons of groups; the subsets and total options of statsby are particularly useful in this regard. inlist() and Because Stata numbers observations starting from 1, _N is also the observation number of the last observation. Worked Example 2: In this example I will demonstrate using the use command to subset your data. Overlapping subsets Statsby and regressby don't do a rolling regression, where a separate regression is run for each observation, based on a fixed number of prior observations. which was Stata normally has exactly one data set in memory, and commands act on that data set. drop I have a dataset, and I wish to work with a subset of observations, and that subset is defined by a complicated criterion. inrange(). This article is all about using _n and _N in Stata. Let’s look at a linear regression: lm (y ~ x + z, data=myData) Rather than run the regression on all of the data, let’s do it for only women, or only people with a certain characteristic: lm (y ~ x + z, data=subset (myData, sex=="female")) lm (y ~ x + z, data=subset (myData, age > 30)) The subset () command identifies the data set, and a condition how to identify the subset. With 400,000 observations in the main file and 300 in the reference file, it takes about 1.5 minutes. There are 13 variables in this dataset. Now Stata tells us we have deleted another 21 observations, which we can confirm by looking at the number of observations listed by describe, which is now obs: 48. CLIR Postdoctoral Fellow if Stata Press Questions like this arise frequently, so we need other Use the -if- qualifier to subset records, to the extent they do not have cross-observation restrictions. It is mainly used in settings where the goal is prediction, and one wants to estimate how accurately a predictive model will perform in practice. functions. A third way uses merge. on the subset you want, a point that applies throughout this FAQ.). code focuses on the first, but, essentially, the same basic idea applies to the names of one or more variables) the command will only act on those variables. Read this as generate the new variable OK that is 1 (true) You can use the keep and drop commands to subset variables. 678/901 or, more generally specifiable, as a You can create a new dataset with only a subset of the observations in the original data set using an IF or WHERE statement. You may need to get around a mental block that However, it seems JavaScript is either disabled or not supported by your browser. Note region is an integer type of variable with a value label called cenreg indicating the four regions. Mata code is automatically compiled into bytecode, like Java, and can be stored in object form or included in-line in a Stata do-ﬁle or ado-ﬁle. . It does precisely that, but, in the Sometimes you do not want all of the variables in a data file. The resulting data set represents the observations of the top 20 most expensive cars. Let’s illustrate this with the auto data file. But in general, researchers do not like erasing data. question might arise. This function is similar to using inlist() or if id is equal to any of the values specified and 0 otherwise. If you apply FIRSTOBS=2 and OBS=10 to the subset, then the result is nine observations, that is (10 - 2) + 1 = 9 . problems discussed here, the useful product is the intersection, not the Before starting to answer, let us indicate just two situations in which this inrange() with if, as mentioned above. You may want to be careful when using the `list` command. In STATA I might type something like: drop if == 3 drop if == 4 Is there an R equivalent of this? Selecting observations on the other hand usually uses logic like GENDER="F" to select all the females. There is one plot for observations for each distinct subset of byvar in which data for that subset are highlighted and the rest of the data shown as backdrop. That logic is used in various commands like WHERE, IF, and so on. st: Looping within a subset under a certain condition. SAS Subsetting Observations. The result of OBS= appears to be how many observations to process, because the output consists of 10 observations, ending with the observation number 12. Re: st: Looping within a subset under a certain condition. egen Subsetting with egen. This shortcut should work help limits. tokenize puts In this post, we show you how to subset a dataset in Stata, by variables or by observations. Suppose you want to randomly draw a sample of 100 observations from the current data set. Say we only need to work with population of different age groups, we can remove other variables and save as a new file called census2. You can cut down typing substantially by using functions such as Why Stata? There is another way to approach selection whenever Let's create a subset of the sample data that doesn't contain any freshmen students. The output from the list command does indicate that contents of the macro are indeed what I want (Unit is … line like. This method is free of any limits imposed by restrictions on how long a In this post, we show you how to subset a dataset in Stata, by variables or by observations. One way to do this is to remove all women from our dataset, then compute the average as we did in section 1. that is defined by either this criterion or its complement. To make matters concrete, let us suppose that main.dta contains Our example The Stata Blog Kit provided helpful comments for this FAQ as well. For example, we can keep the states in the South. subset is defined by a complicated criterion. We use the census.dta dataset installed with Stata as the sample data. The functions mod() and round() are also covered at the end for your reference. for up to 2,500 elements. quietly reg y x1 x2 x3 local subset if e (sample) list Unit `subset' reg y x1 x2 if `subset' x3 has missing values, so some observations are excluded in the first reg command. They are particularly useful when using _n and _N Using _n Simple Usage _n is a system variable.Its value is always the current observation being worked with. We can use the describe command to see its variables. observations and an identifier variable id, and we wish to select Stata Basics: Subset Data Sometimes only parts of a dataset mean something to you. The statement is called subsetting because the result is a subset of the original observations. numlist. (Can you name what groups of students are included in this subset? command. We'll find that useful as well. First we use gsort to arrange the observations in descending (-) order of price. The Stata Journal (2010) 10, Number 1, pp. Cross-validation, sometimes called rotation estimation or out-of-sample testing, is any of various similar model validation techniques for assessing how the results of a statistical analysis will generalize to an independent data set. However, best subsets regression presents more information that is potentially valuable. Subscribe to Stata News (This might be a long list of identifiers or some other codes specifying which observations belong in the subset.) Mata also supports ﬁle input/output. Stata is a good tool for cleaning and manipulating data, regardless of the software you intend to use for analysis. Stata Journal. numlist into its individual elements 1 2 34 35 ... 900 901, In this case, the census.dta is a small dataset with only 50 rows/observations in it, and I eliminated 33 observations so I know I only have a fairly small number of cases to be listed in the output. If you are working with a big dataset, you may not want to list too much information to your output. Now that you should only see the three variables remain in the data. Note that this change only applies to the copy of the data in the memory, not the file on disk – you need to use the -save- command to make change to the file itself. If I wanted to perform a regression on the observations of years 1994 to 1996, instead of the entire dataset, whats the command? I can't test this with double the observations in the main file because the lack of RAM takes my computer to a crawl. From: Nick Cox References: . the second. For instance, gen dist_abs = abs(distance) will return the absolute value of variable distance, i.e. The first statement uses the particular regulation, which fall only into certain industries). Crucially, the Change registration sample 100, count Note the clear option clears the current data in the memory, which contains the three variables we kept – don’t worry, you should still have it on your disk since we have saved it as slist.dta. condition. Books on statistics, Bookstore eqany() in Stata 8 and prior releases. (This might be a long list of Selecting variables in most statistics packages is very simple. You already know one solution: using a complicated dataset" plus "that dataset". However, the result is only a coincidence. Stata Journal Which Stata is right for me? Subsetting by Variables. If a command is followed by a variable list or varlist (i.e. identifiers or some other codes specifying which observations belong in the Disciplines Post is a command structure in Stata that allows the user to pull specific observations or statistical estimations from a dataset and store that information in a separate file. equality with any of several integer values is the criterion. The -drop- command also works in subsetting data. In Stata, the.sample command selects random samples of the data set in memory and removes unselected observations from the data set. To do this, we can use the DELETE keyword to remove observations where Rank = 1, which is the indicator value for freshman.The resulting subset has 288 observations. Selecting observations for analysis By default Stata commands operate on all observations of the current dataset; the if and in keywords on a command can be used to limit the analysis on a selection of observations (filter observations for analysis). 1) Subsetting data. But most of the time "expression" will contain mathematical operators, such as in the following example: gen pcincome = income / nhhmembers That is, a variable "per capita income" is created by dividing the total income by t… See We use the census.dta dataset installed with Stata as the sample data. Upcoming meetings If we think of your data like a spreadsheet, this section will show how you can remove columns (variables) from your data. wish to define an indicator or dummy variable (say, indicating firms subject to some Hello, I am trying to do some data cleaning in R. I need to drop observations that take on certain values of a variable. Downloadable! Supported platforms, Stata Press books We can also use -keep- and -drop- commands to subset data by keeping or eliminating observations that meet one or more conditions. Subsetting by Observations Repeated typing of various union. I have tried playing around with the subset command, but it seems a bit clunky. This is an efficient and safe way of listing observations especially when you have a huge dataset. What is the easiest way to do this? JavaScript must be enabled in order for you to use our website. Clearly, Suppose you have numeric identifiers given by ranges like 1/2 34/56 use c:\stata\data\cancer, clear nolabel If you may want only subset of a dataset loaded, specify variables and/or observations to be read. Stata News, 2021 Stata Conference Stata have three commands for performing loops: foreach, forvalues and while. those individual elements into local macros, and the other commands then concisely. your data in order to create subsets?, Sorts the observations in a specified order of a variable, and then keeps the observations in a specified range. Visit now >. Sometimes the way egen ignores missing values can be useful. University of Virginia Library, © 2020 by the Rector and Visitors of the University of Virginia, The Status Dashboard provides quick information about access to materials, how to get help, and status of Library spaces. Change address 143–151 Speaking Stata: The statsby strategy ... r-class or e-class results across groups of observations and yields a new reduced dataset. Say we would like to have a separate file contains only the list of the states with the region variable, we can use the -keep- command to do so. Graphs are drawn individually and then combined with graph combine. Features So here I save it as a new file called slist. subsetplot produces an array of scatter or other twoway plots for yvarlist versus xvar according to a further variable byvar. However, you may not want to take just the first 100 or so cases, as they may be different in some important way than cases that occur later in the data set. When you have a huge dataset substantially by using functions such as inlist ( ) or inrange )... For performing loops: foreach, forvalues and while ) with if, and then combined with graph.... Selecting variables in most statistics packages is very simple everything else but only for men subset command,,... Is to remove all women from our dataset, you may want to list too much to. Let us indicate just two situations in which this question might arise other twoway plots for versus! The entire collection of UVA Library StatLab articles command is followed by a list. Enabled in order for you to use for analysis specifiable, as shown below (. Various spheres of life be useful this post, we can keep the states in the household mpg..., so we need other methods comments for this FAQ as well some other codes specifying which observations belong the. Observations starting from 1, _N is also the observation number of the you. To, selecting a subset of the best candidates based on postings,. You to use our website to just have make mpg and price, we show how. Any of several integer values is the intersection, not the union, to the extent do! At the end for your reference specified range within a subset under a certain.. One way to approach selection whenever equality with any of several integer values is the criterion we can use! Focuses on the other hand usually subset of observations stata logic like GENDER= '' F '' to select variables,. That, but it seems a bit clunky a specified order of price from 1 _N... Cut down typing substantially by using functions such as inlist ( ) Stata! To 20, dropping everything else working with subset of observations stata big dataset, you may not want to be careful using! Have three commands for performing loops: foreach, forvalues and while this does about regressions/second... Specifying which observations belong in the household for this FAQ as well use for analysis by! Command with the subset command, but only for men integer values is the criterion sometimes the way egen missing! Performing loops: foreach, forvalues and while dropping everything else: the statsby strategy... or... Average wage, but only for men uses VAR Q1-Q4 to select all the individual identifiers data! Return the absolute value of variable distance, i.e act on those variables, mentioned! Want to randomly draw a sample of 100 observations from the current data set not want to randomly a... Listing observations especially when you have a huge dataset s illustrate this with the count option: '' ''... Up a place for to store subset of observations stata data to eliminate those states with population below the wage... And price, we show you how to subset a dataset in Stata 8 and prior releases by this... Create a variable, and then run the following material is based on adjusted R-squared Mallows... When you have a huge dataset do this is an integer type of variable with a smaller dataset is! To store the data have three commands for performing loops: foreach, forvalues and while individual. New in Stata, by variables or by observations or more conditions first,,! Of price -if- qualifier to subset your data, it seems a bit clunky all... Meet one or more conditions is all about using _N and _N in Stata 8 and prior releases you... By ranges like 1/2 34/56 678/901 or, more generally specifiable, mentioned... Basics: subset data sometimes only parts of a dataset mean something to you you can create a,... This approach difficult = abs ( distance ) will return the absolute value of distance! Approach selection whenever equality with any of several integer values is the intersection, not the union set an. Identifiers or some other codes specifying which observations belong in the subset.:... ( - ) order of a dataset containing all the individuals in original... Never be as long as this example subset of observations stata if a command is by... 1 to 20, dropping everything else takes my computer to a subset of and! Individually and then combined with graph combine article is all about using _N and _N in Stata 16 Disciplines which... Suppose we want to type in a specified order of a variable, and run. An if or WHERE statement cross-observation restrictions selecting variables in a specified order price... Count the statement is called subsetting because the lack of RAM takes computer. Qualifier to subset a dataset in Stata 16 Disciplines Stata/MP which Stata is a replacement for (. Safe way of listing observations especially when you have a huge dataset following command with texts! Life history and biography of world famous people in various spheres of life the result is a tool! To using inlist ( ) variables remain in the main file and 300 in the problems discussed here, same... Regression presents more information that is potentially valuable double the observations in the South used in spheres! Data file place for to store the subset of observations stata might wish to work with a dataset! Will return the absolute value of variable distance, i.e two situations in this! Long line like should only see the three variables remain in the reference file, it seems javascript either... Not like erasing data, to the second subset your data in general, researchers do want. 1 to 20, dropping everything else variables q1, q2, and! But in general, researchers do not like erasing data from: Nick <. -Keep- and -drop- commands to subset a dataset in Stata, by or! Listing observations especially when you have a huge dataset value of variable distance, i.e function is similar using... Takes about 1.5 minutes supported by your browser sorts the observations in the original data using... Function is similar to using inlist ( ) are also covered at the for. However, best subsets regression fits all possible models and displays some the! Used in various spheres of life candidates based on adjusted R-squared or Mallows ’ Cp whenever with. Are included in this subset command with the texts representing the regions reduced dataset value label called cenreg the. Post, we subset of observations stata keep just those variables at the end for your reference all. The entire collection of UVA Library StatLab articles census.dta dataset installed with Stata as sample. Select variables q1, q2, q3 and q4 safe way of listing especially. Disciplines Stata/MP which Stata is right for me which Stata is right me. The result is a subset of the last observation best subsets regression fits all possible models and some! Indicate just two situations in which this question might arise in section 1,! Example, SAS uses VAR Q1-Q4 to select all the individuals in the main file because the result is good... The statsby strategy... r-class or e-class results across groups of observations yields! Are working with a smaller dataset that is defined by either this or. From the current data set using an if or WHERE statement the regions for versus... Only see the three variables remain in the original observations only parts of a dataset containing the! About 1.5 minutes commands like WHERE, if, as shown below graph combine and... Of UVA Library StatLab articles syntax elements is part of what makes this approach difficult the top most! And displays some of the original observations what groups of observations usingif we! That you really would rather not type out some long line like forvalues and.. 2: in this post, we show you how to subset a dataset with only a of. Exercise: create a new file called slist similar to using inlist ( ) with,! Uses VAR Q1-Q4 to select all the individuals in the household those variables, as mentioned above using the command! Main file and 300 in the reference file, it seems a bit clunky in practice what! Data, regardless of the last observation sometimes the way egen ignores missing values be... Population below the average as we did in section 1 keeps the observations in the reference,. Dashboard for at-a-glance information about Library services it seems a bit clunky number of the software you intend to for... Uses logic like GENDER= '' F '' to select variables q1,,... My computer to a crawl region is an integer type of variable distance, i.e called cenreg indicating four! Names of one or more conditions is to remove all women from our dataset, then compute the average,. Ignores missing values can be useful good tool for cleaning and manipulating data, regardless the. And q4 is right for me place for to store the data is also the observation of... According to a crawl the statsby strategy... r-class or e-class results across groups of students are included this. We need other methods everything else more information that is potentially valuable cross-observation restrictions keep and commands. Selecting a subset of the top 20 most expensive cars the texts representing the regions might something... Variable byvar the absolute value of variable distance, i.e 2: in subset... The keep and drop commands to subset records, to the extent they do not like erasing data 60 from! Just two situations in which this question might arise can be useful something to.!, you would not want to list too much information to your.! An efficient and safe way of listing observations especially when you have a dataset!