Question

I have a relatively big text file with blocks of data layered like this:

ANALYSIS OF X SIGNAL, CASE: 1
TUNE X =  0.2561890123390808

    Line Frequency      Amplitude             Phase             Error         mx  my  ms  p

1 0.2561890123391E+00 0.204316425208E-01 0.164145385871E+03 0.00000000000E+00   1   0   0   0
2 0.2562865535359E+00 0.288712798671E-01 -.161563284233E+03 0.97541196785E-04   1   0   0   0

(they contain more lines and then are repeated)

I would like first to extract the numerical value after TUNE X = and output these in a text file. Then I would like to extract the numerical value of LINE FREQUENCY and AMPLITUDE as a pair of values and output to a file.

My question is the following: altough I could make something moreorless working using a simple REGEXP I’m not convinced that it’s the right way to do it and I would like some advices or examples of code showing how I can do that efficiently with Ruby.

Answer 1

Generally, (not tested)

toggle=0
File.open("file").each do |line|
    if line[/TUNE/]
        puts line.split("=",2)[-1].strip
    end
    if line[/Line Frequency/]
        toggle=1
        next
    end
    if toggle
        a = line.split
        puts "#{a[1]} #{a[2]}"
    end
end

go through the file line by line, check for /TUNE/, then split on “=” to get last item.
Do the same for lines containing /Line Frequency/ and set the toggle flag to 1. This signify that the rest of line contains the data you want to get. Since the freq and amplitude are at fields 2 and 3, then split on the lines and get the respective positions. Generally, this is the idea. As for toggling, you might want to set toggle flag to 0 at the next block using a pattern (eg SIGNAL CASE or ANALYSIS)