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Re: How to sort and count efficiently?

From: Assaf Gordon
Subject: Re: How to sort and count efficiently?
Date: Sun, 30 Jun 2019 10:08:46 -0600
User-agent: Mutt/1.11.4 (2019-03-13)


On Sun, Jun 30, 2019 at 07:34:19AM -0500, Peng Yu wrote:
> Hi,
> I have a long list of string (each string is in a line). I need to
> count the number of appearance for each string.
> I currently use `sort` to sort the list and then use another program
> to do the count. The second program doing the count needs only a small
> amount of the memory as the input is sorted.
> [...] Does anybody know any better way
> to make the sort and count run more efficiently?

Using awk:

  awk 'a[$1]++ {} END { for (i in a) { print i, a[i] } }' INPUT \
    | sort -k1,1

Or using gnu awk:

  awk 'a[$1]++ {}
       END { n = asort(a) ;
             for (i = 1; i <= n; i++) {
                 print i, a[i]

 - assaf

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