Re: How do I take every 3rd number from a text file?

*To*: mathgroup at smc.vnet.net*Subject*: [mg114289] Re: How do I take every 3rd number from a text file?*From*: Oliver Ruebenkoenig <ruebenko at wolfram.com>*Date*: Tue, 30 Nov 2010 04:03:13 -0500 (EST)

On Sun, 28 Nov 2010, truxton spangler wrote: > On Nov 27, 7:37 pm, cubsfan334 <cubsfan... at gmail.com> wrote: >> Hi, >> >> I've been reading in text files using the following command: >> >> ReadList["file.txt", Word] >> >> However, now I only want to read in every 3rd number, starting with >> the valueI specify. >> >> For example, say I had these values: >> >> 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 >> >> How would I read in every third number, starting with the second >> integer? So the result would look like this: >> >> 1, 4, 7 > > Assuming that the line above is actually a string: "0, 1, 2, 3, 4, 5, > 6, 7, 8, 9" then use StringSplit and Take or Span, e.g. > > tmp = ToExpression@StringSplit["0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ", ", "] > > then > > Take[tmp, {2, Length[tmp], 3}] > > or > > tmp[[2 ;; Length[tmp] ;; 3]] > > A small side note: you can also index from the back with negative numbers e.g. tmp[[ 2;; -1 ;; 3 ]] Take[tmp, {2, -1, 3}] Oliver