Matlab Script to choose data from a long long data file

I'm sorry if this has been answered before, but I would like to ask if somebody has this easy code that could help me to go faster in my work.

All I need, is a code to extract determined data from a huge file.

For example, suppose the file "THING" contains a matrix of 1000x3.

I want to get 1 data of each 4, so it's "THING_REDUCED"= 250x3 values.

How would you do it?

[Matt Kindig]

Can you post the first few lines of the data file, so that we know the format you are working with?

Also, how is the "1 data of each 4" defined? Do you just want every fourth row in the matrix, or do you want to find the mean of every four rows, or the minimum, or?