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Data management

FAQ:		Data management	Search the FAQs:
Last updated:		30 August 2007
Stata release:		10

Questions are listed below in the following categories:

Reading and inputting data
Combining datasets
Memory usage
Data manipulation
4.1 Variable creation
4.2 Short-cuts
4.3 Puzzling results
4.4 Dataset manipulation
4.5 Replacing values or observations
Data reporting
Other
FAQs concerning releases before Stata 10

1. Reading and inputting data

How do I connect to a database by using a Stata plugin?

How do I export tables from Stata?

Can I use ODBC to write to an existing Excel file?

Why do I get rows of missing data when I use infile?

How can I convert other packages' files to Stata format data files?

How do I set up an ODBC Data Source Name for Stata on Mac or Linux/Unix?

Stata is reading in my variables as string instead of numeric. What should I do?

How do I convert date variables into Stata elapsed dates when the numbers run together, like “4151999”?

How do I get information from Excel into Stata?

How can I save a Stata dataset so that it can be read in a previous version of Stata?

Why do I get the error “wrong number of values” when I use insheet to read data from Excel?

How do I use infile to read in fixed-format data?

Can infile read in a hierarchical dataset?

2. Combining datasets

How do you process very large datasets in Stata?

Why does my merge produce a dataset with too many observations?

3. Memory usage

Each morning I have to set my memory size to, say, 20m. The default, 1m, is not sufficient for my data. Is there a way of changing the default setting?

Why do I get the error message “no room to add more observations”?

How big will my dataset be?

How can I use a dataset that is larger than the available RAM?

4. Data manipulation

4.1 Variable creation

How can I sample clusters, not individuals?

How can I identify first and last occurrences systematically in panel data?

How do I deal with a report of repeated time values within panel?

How can I create variables containing percent summaries?

How can I generate a variable containing the last of several dates?

How do I split a string variable into parts?

What is true and false in Stata?

How do I calculate measures such as percent improved minus percent deteriorated?

How do I create variables summarizing for each individual properties of the other members of a group?

How do I create individual identifiers numbered from 1 upwards?

How do I create a variable recording whether any members of a group (or all members of a group) possess some characteristic?

How do I create dummy variables?

4.2 Short-cuts

How do I perform element-by-element operations on matrices?

How can I list, drop, and keep a consecutive set of variables without typing the names individually?

Can I apply the label values command to more than one variable at the same time? I want to attach the same value labels to several variables.

4.3 Puzzling results

How many significant digits are there in a float?

Why does the mod(x,y) function sometimes give puzzling results? Why is mod(0.3, 0.1) not equal to 0?

Why can’t I compare two values that I know are equal?

Why is x>1000 true when x contains missing values?

Why does my do-file or ado-file produce different results every time I run it?

4.4 Dataset manipulation

How can I apply the original value and variable labels after using the reshape command?

How do I calculate the maximum or minimum seen so far in a sequence?

What are regular expressions and how can I use them in Stata?

How do I remove leading or trailing zeros from string variables?

How do I go through the groups of a variable in order of their first occurrence in the dataset?

How can I drop spells of missing values at the beginning and end of panel data?

Is there a way to tell Stata to try all values of a particular variable in a foreach statement without specifying them?

I want to calculate a variable containing weighted group summary statistics, but I do not want to collapse the data and egen does not support weights. How can I do this?

How do I deal with multiple responses?

How can I collapse my dataset and keep the same variable labels?

How do I identify runs of consecutive observations in panel data?

How do I select a subset of observations using a complicated criterion?

How can I save one or more parts of a large dataset?

How do you efficiently define group characteristics in your data in order to create subsets?

How do I perform multiple operations on data records if a condition is met?

I am having problems with the reshape command. Can you give further guidance?

How do I produce a dataset based on all possible pairs of identifiers within each group?

Why doesn't the destring command in Stata include an encode option?

How can I create a dataset (matrix) of means (other stats) of variables from the current dataset?

How do I implement SAS-like ARRAYs in Stata?

4.5 Replacing values or observations

How can I replace missing values with previous or following nonmissing values or within sequences?

How can I replace an observation of a variable with a different observation for another variable?

5. Data reporting

How do I calculate the number of distinct values seen so far?

How do I count the number of distinct strings across a set of variables?

How do I compute the number of distinct observations?

How do I tabulate cumulative frequencies?

How do I list observations in a group that differ on a variable?

Is there a way to put leading zeros in output?

How can I produce a tabulation of a string variable that is listed in logical rather than alphabetical order?

Is there any direct way to save into a new variable the frequencies obtained by applying the command tabulate?

6. Other

How do I identify neighbors of points or areas on a rectangular grid in Stata?

How do I identify leap years in Stata?

Why am I getting an error message that there is "insufficient disk space"?

How can I put the current date and time in my log files?

How do I accumulate the results of immediate commands?

Why does the command complain that there are no observations?

7. FAQs concerning releases before Stata 10

Is there a way to tell Stata to try all values of a particular variable in a for statement without specifying them?

How do I identify duplicate observations in my data?

How can I convert other packages' files to Stata format data files?

What do I do if the command I need cannot be used with by?

How do I create a variable that contains a repeating sequence of numbers?

I am having trouble converting a SAS dataset to a Stata dataset using Stat/Transfer. What is wrong?

What is the new reshape command?

Why does reshape give a too-many-variables error?

How do I create a lag variable?

How do I make date variables?

Why am I getting a message that there is no room on my hard drive?

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