CSV Comparator is a free to use tool for comparing files which contain CSV-Data. It was created for performance engineers to be able to have a easy way to compare data from two testruns and be able to automate the comparing process of various files with scripts. There is a command line tool as well as a user interface.
In case you need to compare .xml-Files you can convert them to .csv-Files with my other project CSV Transformer.
The advantages by using CSV as input and output are the following:
Many applications allow an export of its data to CSV or Excel(were it could be saved to CSV)
It is possible to pre- and postprocess the data, e.g removing version numbers before comparing
It is easy to create CSV data from logfiles and other resources by using unix tools like sed or awk
CSV can be loaded into other applications, especially Excel, were it can be formatted by macros for analyzing.
Comparing .csv-Files column-wise
Compare difference, difference in percentage or as strings
Reading files with any delimiter, with or without quotes
Making row identifiers unique before comparing
Divide/Multiply values before comparing
Comparing .csv-Files containing sections of data (see top level feature)