Summary

ADD FILES is an SPSS command that's mainly used for merging data sources holding similar variables but different cases. (For the same cases but different variables, see MATCH FILES.) A second use is for reordering and/or dropping variables in a single dataset. SPSS Add Files Matches Data Sources on Variable Names

SPSS Add Files - Basic Usage

The ADD FILES command illustrated in the screenshot above results from running the syntax below.

SPSS Add Files Syntax Example

SPSS Add Files Rules

• Up to 50 datasets or data files can be merged with a single ADD FILES command.
• ADD FILES can also be used for reordering and/or dropping variables in a single dataset. This is done by using the KEEP or DROP subcommand. How it works is explained in MATCH FILES.

SPSS Add Files Pitfalls

• If a variable has inconsistent dictionary information across data sources, you may end up with nonsensical data. This is explained in SPSS Recode - Cautionary Note. For a tool that detects dictionary inconsistencies over files, see Compare Dictionaries over Files Before Merging.
• If there are string variables present, they should have the same lengths across all data sources. Adjust String Lengths before Merging Files shows how to do this automatically using Python.
• Especially with many data files, you may want to add the file names as a new variable to the files. Like so, you can easily see the source of each case in the merged data. See Add Filenames to Files Before Merging.
• An alternative for adding the data sources to the merged result is using the IN subcommand as in add files file d1 /in = d1 / file d2 /in = d2.
• If you want to merge a lot of files, you can have Python do it for you. This is demonstrated in !!0250.