Various steps are required to allow factor variables to be specified with a command and to correctly handle the new collinearity behavior. Oct 19, 2012 discover factor variables and a basic introduction to using them in regression models. I am aware that if product were a numeric variable we could use the collapse command. All indicator variables are categorical variables, but the opposite is not true. String variables can have a length of 1 to 244 characters. I have completed the principal component analysis pca, exploratory factor analysis efa, and confirmatory factor analysis cfa, treating data with likert scale 5level responses. On april 23, 2014, statalist moved from an email list to a forum, based at. The main problems that may arise and their possible solutions are surveyed with reference both to official stata and to userwritten programs. Keywords pr0006, binary variables, categorical variables, data editor, dates, decode, destring, encode, identifiers, missing values, numeric variables, spreadsheets, string functions, string. Encode assigns numerical values 1, 2, to newvar, while the original values e. If you have more than 67,784 unique values of the string variables that you are encoding, encode will complain. You cant use numeric functions such as addition or subtraction on string variables. Reed college stata help changing string variables to.
Christopher f baum boston collegediw factor variables and marginal effects jan 2010 7 18. Command generate is used if a new variable is to be added to the data set. There are no system missing values in string variables. Then, using lavaan, i repeated the cfa defining the variables as categorical. Stata news, code tips and tricks, questions, and discussion. The command set more off tells stata not to pause or display the more message. This can be helpful even if factor variables are not specified. This allows you to specify how you would like missing values in.
In order to see what a string variable looks like, we can use the converse command. String variables that seemingly should be numeric require some care. We are here to help, but wont do your homework or help you pirate software. Create factor dummy variables from a long variable statalist.
The first tabulate looks identical to the tabulate done on the string variable region above. Stata is a complete, integrated software package that provides all your data science needsdata manipulation, visualization, statistics, and automated reporting. They have an added benefit in that postestimation commands better understand the components of your model. How can i convert string variables into date variables. Transform string variable to categorical integer variable. This command can replace loops where a manual check is done to see if the specified variable is contained in eb andor ev. Press question mark to learn the rest of the keyboard shortcuts.
An example of when one might need to do this is if they needed to append. Sep 27, 2016 convert variables from string to numeric in stata duration. Categorical variables refer to the variables in your data that take on categorical values, variables such as sex, group, and region. This is the eighth post in the series programming an estimation command in stata.
All variables in the working file or in variable sets in use are inappropriate for this. Using stata efficiently to understand your data the analysis factor. Cs6, cs6 is just a variable for education completed, but every time i try to run this regression, it says cs6. Spss string function converts numeric values to string values. Factor variables refer to statas treatment of categorical variables. When cleaning datasets one often has string variables containing categories e. Learning to use statistical software involves a lot of trial and error, angry. Like so, working with string variables in spss is super easy. As you can see from the second tabulate, region2 has the numeric values 1 through 4 but retains the strings central, east, south and west as value labels. Now, lets say you would like to create a categorical variable that tells you. But i dont think theres a command that extracts the level or base level of a factor variable or that splits a factor variable into its variable name and level. I have a data file which contains string variables only.
Some of these are the following use help function in stata to learn more. When i run this from my dofile, after the first set of dydx output i get the. This also influences the results of functions such as strlen. Odd numbers of characters in string variables were soon allowed in stata 2. Why cant i see my variables in some of the spss dialog boxes. Previously i used the code cor x1 x2 when finding the correlation between continuous variables but i am not sure how to proceed when dealing with categorical variables. I know somebody has asked this question before, but i found the answers to be unhelpful. To create new variables typically from other variables in your data set, plus some arithmetic or logical expressions, or to modify variables that already exist in your data set, stata provides two versions of basically the same procedures. There are a number of advantages to converting categorical variables to factor variables. Complex strings may be very long and may contain binary information. But with statas datetime features, some computations, as well as the representation of data to the human eye and mind may become easier.
In stata this is often true because stata treats string encoded variables as missing and will not use them in analyses. If the variable is actually a numeric value that just happens to be stored as a string, see our faq. A simple way of transforming such a variable to one variable containing the same information is encode. Factor scores in approaches 2 and 3 are more difficult to estimate than factor scores in classic fa or in approach. You can, however, extract one or more characters a substring from them, glue them together concatenate and a couple of other functions. I may have possible issues with multicolinearity and i want to check. If syntax varlist is used and factor variables are to be allowed in the varlist. Irt fitting certainty quickly decreases as the number of factors grows, which is a problematic side of this approach. One method of converting numbers stored as strings into numerical variables is to use a string function called real that translates numeric values stored as strings into numeric values stata can recognize as such. However, when i click on analyze multiple response define variable sets i get a popup window with a warning. Perhaps the most important advantage is that they can be used in s. Stata is not sold in modules, which means you get everything you need in one package.
It is obsolete xi has been replaced by explicit support for factor variables since stata 11 and numerically cumbersome use xtreg, fe or areg instead. Christopher f baum boston collegediw factor variables and marginal effects jan 2010 7. But i do not want those variables to be treated as factor variables. Merging string variables into one variable statalist. I hope that made sense, i might not even be understanding how stata does panel data correctly. However my variables are categorical and coded 0, 1, 2, 4 etc. However, anticipating that this may be problematic, stata offers various commands to change string variables into categorical variables and vice versa. Choose which interaction to omit using factor variables and fixed effects hot network questions product of 2 uniform random variables is greater than a constant with convolution. The first line of syntax reads in the dataset shown above. I think thatd likely work well as long as cross operators arent used, for example, c. Before we do this, we take a random sample of 10% of the cusips. As an example, the german word fur is a string of length three in stata, but the string length is four in stata 14. As strlen refers to the memory used and not the number of characters as they appear on the screen, the result of strlenfur will also be 4 in stata 14 in.
The easiest way to convert string variables to numeric form is to use the encode command. So long as you have the variables that you used in creating the dummy variables, i consider it much more appealing to import your entire dataset into stata and generate the dummy variables there. Next, we populate the new string variables using the compute command with the substr function. The string variables represent answers to multiple response questions and are either dichotomous or categorical answers coded as strings. Jul 28, 2009 when cleaning datasets one often has string variables containing categories e. Dates in string form, identifiers and categorical variables, and pure numeric content trapped in string form need different actions. The first case most often occurs when importing data from another source.
Listing nonmissing string variables in stata stack overflow. Changing string variables to categorical variables and vice verse. I modify the ordinary leastsquares ols command discussed in programming an estimation command in stata. Stata as well as most other statistical packages wont use observations that are. Generating dummy variables from excel file into stata. The following document provides an example of how to create. Since both are of the form 22xxx, i want to assign value 1 for both in the variable. Spearman 1904 appears to be the rst to conjecture that a common unobserved trait mental ability may be responsible for the positive correlation in. However, they cant be used for new string variables. The variables may contain numeric values, but if they are defined as type string, there are very few things you can do to analyze the data. The next thing i like to know about my data is if any of the variables are string. Also factor variables are supported in most official stata commands, and communitycontributed commands will need to understand this new syntax for factor variables to be accepted. You can only tell the type of a variable by using the describe command.
Also, please do not use this syntax to estimate fixed effects regressions. You cannot get means, you cannot do a regression, you cannot do an anova, etc. The column provides a stepbystep guide explaining how to convert them oras the case may meritto leave them as they are. Entering factor variables in regressions in stata factor variables are a way to quickly enter dummy variables or interactions in a regression model in stata without creating new variables first.
There may be times that you receive a file that has many or all of the variables defined as strings, that is, character variables. Again, im new to stata, but how woud i go about telling stata to treat a flight, or any x variable, as only explaining a change in the y variable a week or so later. How can i easily convert a string variable to a categorical. One possible reason is that your variable is a string variable and the dialog box will only accept numeric variables.
Note that modern statistical software offers a tremendous range of possibilites. One or more spaces, despite usually conveying nothing to people, do not qualify as missing so far as stata is concerned. Ibm i cannot use string variables for creating a multiple. In the third step, we create numeric versions of the string variables using the compute command with the numeric function. Jun 18, 2016 factor variables are categorical variables that can be either numeric or string variables. In earlier versions, a string variable could contain up to 244 characters. Stata handles factor categorical variables elegantly. Data analysis with python and pandas convert string category to numeric values tutorial 6. With string variables, stata has only one definition of missing, namely that a string is empty, and contains precisely no characters. I have a dataset with string variables and i am trying to generate a new binary variable based on the first two characters.
Factor variables are categorical variables that can be either numeric or string variables. Now that we know the variables are string variables, we can use the list. Unless you have a very old version of stata, in which case you should be telling us about it, use factor variable notation, not explicit indicator. Even so, because the variable is defined as str2, stata cannot perform any kind of. This allows you to specify how you would like missing values in a string variable to b handled when autorecoded. There are a few reasons why you may not be able to see your variables in some of the spss dialog boxes. In stata this is often true because stata treats stringencoded variables as missing and will not use them in analyses. In stata this is often true because stata treats stringencoded variables as missing and. Even though this is not typical, this variable may also appear on the right. Alternatively, you can use encode to convert string categorical variables to. I want to collapse the data in stata such that the data appears as.
These variables can be used like any other numeric variables. All strings are 5 characters long, but im only concerned with the first two in order to sort. However, i dont know what to do in this situation since product is a string variable. Another possibility is that your variable has a different measurement. And, you can choose a perpetual licence, with nothing more to buy ever. Why is my command not working with factorvariable syntax andor collinear. These string variables can be used in creating row labels for output tables andor plots, possibly using the sencode package. The following document provides an example of how to. It seems that stata automatically treat some data as factor variables. A complex string is a string that contains more than one piece of information. Commands that pass values into variables, most notably compute and if, can be used for both existing and new numeric variables. Lastly, omission of variables is not an error, but intended behavior when the design matrix is singular.
Discover factor variables and a basic introduction to using them in regression models. A better ols command to allow for sample restrictions, to handle missing values, to allow for factor variables, and to deal with perfectly collinear variables. To start this process, we first create the three string variables called m1, d1 and y1. This module may be installed from within stata by typing ssc install factmerg. How can i quickly convert many string variables to numeric. If you have a string variable and want to convert it to a numeric variable, you can use the encode command. Stata will assume that both variables are to be treated as categorical if there is no prefix. Stata module to merge a list of factors to create string variables, statistical software components s419602, boston college department of economics, revised 20 apr 20. How can i quickly convert many string variables to numeric variables.
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