Preparation of Data Files

Before analysis can commence, the data must be loaded into PSPP and arranged such that both PSPP and humans can understand what the data represents. There are two aspects of data:

The variables—these are the parameters of a quantity which has been measured or estimated in some way. For example height, weight and geographic location are all variables.
The observations (also called 'cases') of the variables—each observation represents an instance when the variables were measured or observed.

For example, a data set which has the variables height, weight, and name, might have the observations:

1881 89.2 Ahmed
1192 107.01 Frank
1230 67 Julie

The following sections explain how to define a dataset.

Defining Variables

Variables come in two basic types: "numeric" and "string". Variables such as age, height and satisfaction are numeric, whereas name is a string variable. String variables are best reserved for commentary data to assist the human observer. However they can also be used for nominal or categorical data.

The following example defines two variables, forename and height, and reads data into them by manual input:

PSPP> data list list /forename (A12) height.
PSPP> begin data.
data> Ahmed 188
data> Bertram 167
data> Catherine 134.231
data> David 109.1
data> end data
PSPP>

There are several things to note about this example.

The words data list list are an example of the DATA LIST. command, which tells PSPP to prepare for reading data. The word list intentionally appears twice. The first occurrence is part of the DATA LIST call, whilst the second tells PSPP that the data is to be read as free format data with one record per line.

Usually this manual shows command names and other fixed elements of syntax in upper case, but case doesn't matter in most parts of command syntax. In the tutorial, we usually show them in lowercase because they are easier to type that way.
The / character is important. It marks the start of the list of variables which you wish to define.
The text forename is the name of the first variable, and (A12) says that the variable forename is a string variable and that its maximum length is 12 bytes. The second variable's name is specified by the text height. Since no format is given, this variable has the default format. Normally the default format expects numeric data, which should be entered in the locale of the operating system. Thus, the example is correct for English locales and other locales which use a period (.) as the decimal separator. However if you are using a system with a locale which uses the comma (,) as the decimal separator, then you should in the subsequent lines substitute . with ,. Alternatively, you could explicitly tell PSPP that the height variable is to be read using a period as its decimal separator by appending the text DOT8.3 after the word height. For more information on data formats, see Input and Output Formats.
PSPP displays the prompt PSPP> when it's expecting a command. When it's expecting data, the prompt changes to data> so that you know to enter data and not a command.
At the end of every command there is a terminating . which tells PSPP that the end of a command has been encountered. You should not enter . when data is expected (ie. when the data> prompt is current) since it is appropriate only for terminating commands.

You can also terminate a command with a blank line.

Listing the data

Once the data has been entered, you could type

PSPP> list /format=numbered.

to list the data. The optional text /format=numbered requests the case numbers to be shown along with the data. It should show the following output:

           Data List
┌───────────┬─────────┬──────┐
│Case Number│ forename│height│
├───────────┼─────────┼──────┤
│1          │Ahmed    │188.00│
│2          │Bertram  │167.00│
│3          │Catherine│134.23│
│4          │David    │109.10│
└───────────┴─────────┴──────┘

Note that the numeric variable height is displayed to 2 decimal places, because the format for that variable is F8.2. For a complete description of the LIST command, see LIST.

Reading data from a text file

The previous example showed how to define a set of variables and to manually enter the data for those variables. Manual entering of data is tedious work, and often a file containing the data will be have been previously prepared. Let us assume that you have a file called mydata.dat containing the ascii encoded data:

Ahmed          188.00
Bertram        167.00
Catherine      134.23
David          109.10
              .
              .
              .
Zachariah      113.02

You can can tell the DATA LIST command to read the data directly from this file instead of by manual entry, with a command like: PSPP> data list file='mydata.dat' list /forename (A12) height. Notice however, that it is still necessary to specify the names of the variables and their formats, since this information is not contained in the file. It is also possible to specify the file's character encoding and other parameters. For full details refer to DATA LIST.

Reading data from a pre-prepared PSPP file

When working with other PSPP users, or users of other software which uses the PSPP data format, you may be given the data in a pre-prepared PSPP file. Such files contain not only the data, but the variable definitions, along with their formats, labels and other meta-data. Conventionally, these files (sometimes called "system" files) have the suffix .sav, but that is not mandatory. The following syntax loads a file called my-file.sav.

PSPP> get file='my-file.sav'.

You will encounter several instances of this in future examples.

Saving data to a PSPP file.

If you want to save your data, along with the variable definitions so that you or other PSPP users can use it later, you can do this with the SAVE command.

The following syntax will save the existing data and variables to a file called my-new-file.sav.

PSPP> save outfile='my-new-file.sav'.

If my-new-file.sav already exists, then it will be overwritten. Otherwise it will be created.

Reading data from other sources

Sometimes it's useful to be able to read data from comma separated text, from spreadsheets, databases or other sources. In these instances you should use the GET DATA command.

Exiting PSPP

Use the FINISH command to exit PSPP: PSPP> finish.

GNU PSPP