Category: Stata trim string


There may be times that you receive a file that has many or all of the variables defined as stringsthat is, character variables. The variables may contain numeric values, but if they are defined as type stringthere are very few things you can do to analyze the data. You cannot get means, you cannot do a regression, you cannot do an ANOVA, etc… Sometimes the dataset contains numerical values that are stored as strings.

We will address this scenario first. Then we will address the case where the string variables actually contain strings, and the goal is to assign each value the string takes on to a numeric value. The example dataset, hsbsis a subset of the High School and Beyond data file with all of the variables as string variables.

As you see from the describe command below, the variables are all defined as string variables e. Now that we know the variables are string variables, we can use the list command to see what the strings stored in these variables look like. Although the variable science is defined as str2, you can see from the list below that it contains just numeric values.

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Even so, because the variable is defined as str2, Stata cannot perform any kind of numerical analysis of the variable science. The same is true for the variable read. 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.

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The first line of syntax reads in the dataset shown above. The real s is the function that translates the values held as strings, where s is the variable containing strings. A second method of achieving the same result is the command destring.

The first line of syntax loads the dataset again, so that we are starting with a dataset containing only string variables again. The second line of syntax runs the destring command. As you can see from the describe command below, the destring command converted all of the variables to numeric, except for racegender and schtyp. Since these variables had characters in them, the destring command left such variables alone. If there had been any numeric variables in the dataset, they would remain unchanged.

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Both of the techniques described above have attributes that in some situations are advantages and in other situations may be disadvantages. To some extent destring can be made to behave similarly, but not identically. In order to convert a string variable containing any non-numeric value using destring one must list the characters that should be ignored e.

How do we convert gender and schtyp into numeric values? We can use the encode command as shown below. These commands create gender2 and schtyp2. Notice in the describe command below that gender2 and schtyp2 are numeric variables and they have labels associated with them called gender2 and schtyp2. If we list out the data, it appears that gender2 and schtyp2 are identical to gender and schtyphowever they are really numeric and what you are seeing are the value labels associated with the variables.

Below we use the nolabel option and you see that gender2 and schtyp2 are really numeric.String processing is fairly easy in Stata because of the many built-in string functions. Among these string functions are three functions that are related to regular expressions, regexm for matching, regexr for replacing and regexs for subexpressions.

At the bottom of the page is an explanation of all the regular expression operators as well as the functions that work with regular expressions.

Example 1: A researcher has addresses as a string variable and wants to create a new variable that contains just the zip codes. Example 2: We have a variable that contains full names in the order of first name and then last name. We want to create a new variable with full name in the order of last name and then first name separated by comma. Example 2: Dates were entered as a string variable, in some cases the year was entered as a four-digit value which is what Stata generally expects to seebut in other cases it was entered as a two-digit value.

We want to create a date variable in numeric format based on this string variable. We have included this example here for demonstration purposes, not because regular expressions are necessarily the best way to handle this situation. In these situations, regular expressions can be used to identify cases in which a string contains a set of values e.

To find the zip code we will look for a five-digit number within an address. The gen command short for "generate" below tells Stata to generate a new variable called zip.

This means that stringing five of these expressions together will enable us to find a string of exactly five digits.

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Note that the indicates that the expression should match any character 0 through 9 i. In our simplified example above, none of the addresses have five-digit street numbers. What if there are addresses with five-digit street numbers? Apparently, this is not working correctly since the last two rows of the variable zip have picked up the street numbers for these addresses instead of zip codes. In this data set, the zip code appears at the end of the address string.

If we assume that this the case for all addresses in the data, the remedy will be really simple. Sometimes zip code also include the four-digit extension and the country name may also appear at the end of the address, such as in some of the addresses shown below.

Here is how we can do it using a more complicated regular expression. There are three components in this regular expression. These additions allow us to match up the cases where there are trailing characters after the zip code and to extract the zip code correctly. Notice that we also used "regexs 1 " instead of "regexs 0 " as we did previously, because we are now using subexpressions indicated by the pair of parenthesis in " [][][][][] ".

Another strategy that might work better in some cases is the regular expression. In this example, the period i. Together, the two indicate that the number we are looking for should not occur at the very beginning of the string, but may occur anywhere after.

Cleaning up messy (string) variables

We want to create a new variable for full name in the order of last name and then first name separated by comma. Now we need to capture the first word and the second word and swap them. This indeed works. The following code uses regexs to place each of these components subexpressions into its own variable and then displays them.

In this example, we have dates entered as a string variable. Stata can handle this using standard commands see " My date variable is a string, how can I turn it into a date variable Stata can recognize? The goal of this process is to produce a string variable with the appropriate four digit year for every case, which Stata can then easily convert into a date.

To do this we will start by separating out each element of the date day, month, and two- or four- digit year into a separate variable, then we will assign the correct four-digit year to cases where there are currently only two digits, finally, we concatenate the variables to create a single string variable that contains month, day, and four-digit years.

Next, we want to identify the day of the month and place it in a variable called day.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information.

For example, I have observations and I want to drop the 30 highest ones. Is there a command for this kind of trimming? Btw, I am new to Stata. Learn more. Trimming data in Stata Ask Question. Asked 6 years, 8 months ago. Active 4 years, 5 months ago. Viewed 10k times. Nick Cox 27k 5 5 gold badges 24 24 silver badges 43 43 bronze badges. MarMarko MarMarko 35 2 2 gold badges 3 3 silver badges 9 9 bronze badges.

Just to point out what should be obvious: Many statistical people consider this kind of dropping of data to be a bad idea. A related but different point is that this is not trimming in the sense of e. Active Oldest Votes.

Metrics Metrics Peter Dutton Peter Dutton 1 1 silver badge 11 11 bronze badges. Vivek Vivek 1 1 silver badge 17 17 bronze badges.

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This is misleading as an answer without an explanation that you must sort first and separately deal with missing values. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Socializing with co-workers while social distancing. Podcast Programming tutorials can be a real drag.Documentation Help Center.

However, strtrim does not remove significant whitespace characters. For example, strtrim removes leading and trailing space and tab characters, but does not remove the nonbreaking space character, char Create a character vector with spaces and a tab character as leading whitespace.

stata trim string

Starting in Ra, you can create strings using double quotes. Create a string array, and remove leading and trailing whitespace with the strtrim function. Remove the leading and trailing whitespace from all the character vectors in a cell array and display them. Create a character vector that includes the nonbreaking space character, charas a trailing whitespace character.

Coding of String Variable in STATA

Display chr between symbols to show the leading and trailing whitespace. Display newChr between symbols. Input text, specified as a character array or as a cell array of character arrays, or a string array. This table shows the most common characters that are significant whitespace characters and their descriptions. For more information, see Whitespace character.

This function fully supports tall arrays. For more information, see Tall Arrays. A modified version of this example exists on your system. Do you want to open this version instead? Choose a web site to get translated content where available and see local events and offers. Based on your location, we recommend that you select:. Select the China site in Chinese or English for best site performance. Other MathWorks country sites are not optimized for visits from your location.

stata trim string

Toggle Main Navigation. Search Support Support MathWorks. Search MathWorks. Off-Canvas Navigation Menu Toggle. Open Live Script. Keep Nonbreaking Space Character. Input Arguments collapse all str — Input text character array cell array of character arrays string array. Algorithms strtrim does not remove significant whitespace characters. Significant Whitespace Character Description char Next line char Nonbreaking space char Figure space char Narrow no-break space.

Extended Capabilities Tall Arrays Calculate with arrays that have more rows than fit in memory. Usage notes and limitations: Input text must be string scalar or a character array. Input values must be in the range 0—Why Stata? Supported platforms. Stata Press books Books on Stata Books on statistics.

Policy Contact. Bookstore Stata Journal Stata News. Contact us Hours of operation. Advanced search. I want to split a string variable. The variable case names court cases, and I would like to have separate variables for plaintiff and defendant. They are divided by "V" or "VS" or "V. The number of words on either side of the divide is not constant. If you have Stata 7, a previous version of split is available from SSC, and you can bail out now, unless you too want to keep reading. This is a nice example of how a problem can be easy for people to specify.

The challenge is to translate it into Stata. For example, although egen provides several functions for subdividing string variables, this problem, like many others, is best tackled by using the basic string functions. We need first to find the position of " V " or " VS " or " V. Use the function strpos. In Stata 8, this function was called index. Thus strpos "frog toad", "o" is 3 because the first occurrence of "o" starts at the 3rd character of "frog toad".

If there is no such occurrence, the result is 0. The string we search for includes surrounding spaces. If this is true, we have a problem somewhere, perhaps a typo has occurred, the dividing element was left out, or someone used lowercase. With a few problems, it might be easiest to do small-scale surgery within the editor.

In problems with mixtures of case, the functions upper and lower come in handy. We can rely on Stata to work out the appropriate string type when it replaces plaintiff by the desired string.

For example, an alternative would be. The substr function has three arguments: the string, or string variable, from which we copy a substring; the position of the start of the substring; and the length of the substring to be copied. A period. But we still want to strip the "V ""VS ""V.

Let us look at the arguments to substr more closely. That is.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time.

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stata trim string

What I would like to do, is to take the first part of the string before the - symbol. For future questions, please post attempted code and why it's not working for you. Questions asking only for code are deemed off-topic by some users. This takes the substring of variable degree starting in position 1, and ending in the position minus 1 in which the first - is found.

If there is no - in the original variable, a missing will be generated so a replace is in place. See help string functions for an array of functions that can be used to manipulate strings. Previous answers using substring and split are probably better in Stata.

I am posting a regular expression solution just for completeness. Then you can get required sub String by its index.

stata trim string

One could also use the egen command with its ends function and the associated punct option:. Learn more. How to get a substring that ends before a certain symbol Ask Question. Asked 5 years, 8 months ago. Active 1 year, 10 months ago. Viewed 4k times. For example, from the first three lines I need to get Bachelor of Commerce. I would appreciate if somebody could tell me the easiest way to do it. Pearly Spencer 1. George Matthews George Matthews 25 1 1 silver badge 4 4 bronze badges.

Active Oldest Votes. Dimitriy V. Masterov Dimitriy V. Masterov 8, 1 1 gold badge 19 19 silver badges 42 42 bronze badges. Roberto Ferrer Roberto Ferrer Aspen Chen Aspen Chen 3 3 silver badges 9 9 bronze badges. Masterov Jul 30 '14 at Thanks for pointing that out. Apparently the negation still works in Stata even though it is not official.

How can I quickly convert many string variables to numeric variables? | Stata FAQ

Other suggestions? I did not mean to imply that it did not work. It certainly does!Working on firm level data againI have the experience of cleaning up hundreds of different spelinngs of occupations that should eventually be categorized into a set of occupations that should only differ when actual different occupations are needed. Let me call the variable occupation. One of the problems is that occupations might be capitalized differently, i.

More problematic are white space within a string, or at the beginning and end. Quite typical for variables that come from typists, or systems that do not enforce a common coding. However, these differences are hard to find, even browsing through the data. View all posts by kriechel. You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account. You are commenting using your Facebook account. Notify me of new comments via email.

Notify me of new posts via email. This site uses Akismet to reduce spam. Learn how your comment data is processed. Skip to content Working on firm level data againI have the experience of cleaning up hundreds of different spelinngs of occupations that should eventually be categorized into a set of occupations that should only differ when actual different occupations are needed.

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