bash - How can I delete every Xth line in a text file?

Question

Consider a text file with scientific data, e.g.:

5.787037037037037063e-02 2.048402977658663748e-01
1.157407407407407413e-01 4.021264347118673754e-01
1.736111111111111049e-01 5.782032163406526371e-01

How can I easily delete, for instance, every second line, or every 9 out of 10 lines in the file? Is it for example possible with a bash script?

Background: the file is very large but I need much less data to plot. Note that I am using Ubuntu/Linux.

Answer 1

This is easy to accomplish with awk.

Remove every other line:

awk 'NR % 2 == 0' file > newfile

Remove every 10th line:

awk 'NR % 10 != 0' file > newfile

The NR variable in awk is the line number. Anything outside of { } in awk is a conditional, and the default action is to print.