1.0 SPSS commands used in this unit
|select if||keeps selected cases in the data current data file|
|descriptives||procedure for obtaining means, standard deviations, etc.|
|save outfile||saves the current data file with a new name|
|display||displays requested file information|
|add files||appends (stacks) data files (adds cases)|
|sort cases||sorts cases in the data file|
|match files||merges data files (adds variables)|
2.0 Demonstration and explanation
In this unit we will illustrate methods for subsetting data (in other words, using only some of the cases), appending data (adding cases from another SPSS data file), and merging data (adding variables from another SPSS data file).
2.1 Subsetting cases
Let’s open the data file.
get file "c:spss_datahs1.sav".
Let’s pretend that we are working on our honors thesis and that we want to study just "good readers", those with reading scores 60 or higher. We will open the file and then "select cases" to include the students with reading scores of 60 or higher.
* keeping cases for which students have a reading * score of 60 or higher. select if read >=60. descriptives /var=read.
Notice that the undesired cases have now been deleted. Now we will save our data.
* saving the data file. save outfile "c:spss_datahsgoodread.sav".
2.2 Subsetting variables
Let’s open the hs1 data file again.
get file "c:spss_datahs1.sav".
We want to keep just some variables, including id female read and write. We keep these variables in the same procedure that we use to save the data file. Notice you can also choose keep all if that is more helpful to you.
* pretend we have 2000 variables and we want to keep just * some of the variables. We want to keep just the variables * id female read write. save outfile = "c:spss_datahskept.sav" /keep=id female read write. display names.
Let’s suppose we are working on our masters thesis. There are two files, one for the males (hsmale.sav) and one for the females (hsfemale.sav). We would like to combine these files. We will start by opening the file with the data for the males.
* have one file with males, females in another file * and need to "append" the files. get file "c:spss_datahsmale.sav".
As we can see, the variable female (which indicates gender) is a constant. This is what we would expect in a file with data only for males.
Now we can append the files.
add files /file=* /file="c:spss_datahsfemale.sav".
We will now save the data file with a new name.
save outfile "c:spss_datahsmasters.sav".
Now let’s suppose that we are working on our dissertation. The data are in two files, one with the demographic information (hsdem.sav) and one with the test scores (hstest.sav). We would like to match merge these files based on id. Before we can match merge these files, we need to open each file, sort it on id, and then save the sorted file.
* one file has demographic information, the other has * test scores and we want to "match merge" the files. get file "c:spss_datahsdem.sav". sort cases by id. save outfile "c:spss_datahsdem.sav".
Now that we have sorted and saved the first file (hsdem.sav), we will do the same thing
for the second file (hstest.sav).
get file "c:spss_datahstest.sav". sort cases by id. save outfile "c:spss_datahstest.sav".
Finally, we will open the first file (hsdem.sav) and merge it with the second file (hstest.sav). We will save the merged data file with the name hsdiss.sav.
get file "c:spss_datahsdem.sav".
It is important that we merge the data sets by the same variable on which we sorted the two files.
match files /file=* /in=fromdem /file="c:spss_datahstest.sav" /in=fromtest /by id.
Finally, we will save the data file with a new name.
save outfile "c:spss_datahsdiss.sav".
3.0 For more information
- SPSS Programming and Data Management, Fourth Edition
- Chapter 4
- SPSS Learning Modules
Concatenating data files
Match merging data files