From: Robert Citek <robert.citek@...>
Date: 2007-12-21T00:28:08+09:00
Subject: Re: slicing in ruby

On Dec 20, 2007 2:40 AM, Robert Klemme <shortcutter@googlemail.com> wrote:
> 2007/12/20, Robert Citek <robert.citek@gmail.com>:
> > Found it: indices, which is deprecated in favor of values_at.
> >
> > $ echo $(seq 1 10) | tee /dev/stderr |  ruby -lane 'print
> > $F.values_at(1,2,3,8,2,2).join(" -- ") '
> > 1 2 3 4 5 6 7 8 9 10
> > 2 -- 3 -- 4 -- 9 -- 3 -- 3
>
> Why not
>
> $ ruby -e 'a=(1..10).to_a; $stderr.puts(a.join(" ")); puts
> a.values_at(1,2,3,8,2,2).join(" -- ")'
> 1 2 3 4 5 6 7 8 9 10
> 2 -- 3 -- 4 -- 9 -- 3 -- 3
>
> ?

First, thank you for the example.  Made me wonder about the .to_a
method and discover that 1..10 works differently in ruby than in perl:

$ perl -le 'print 1..10'
12345678910

$ ruby -le 'print 1..10'
1..10

To answer your question: because 'echo $(seq 1 10)' represents the
abstract "any delimited input data" model, which could be multi-line,
thus the -lane options.  Also, because I tend to build up my
quick-and-dirty scripts from the command line: first head the file,
then filter/modify the data stream, repeat quickly.  So the example
above is merely one in a series of commands:

$ seq 1 10
$ echo $(seq 1 10)
$ echo $(seq 1 10) | tee /dev/stderr
$ echo $(seq 1 10) | tee /dev/stderr |  ruby -lane 'print $F'
$ echo $(seq 1 10) | tee /dev/stderr |  ruby -lane 'print $F.join(" -- ") '
$ echo $(seq 1 10) | tee /dev/stderr |  ruby -lane 'print $F(1,2).join(" -- ") '
$ echo $(seq 1 10) | tee /dev/stderr |  ruby -lane 'print
$F[1,2,3].join(" -- ") '
$ echo $(seq 1 10) | tee /dev/stderr |  ruby -lane 'print
$F.values_at(1,2).join(" -- ") '
$ echo $(seq 1 10) | tee /dev/stderr |  ruby -lane 'print
$F.values_at(1,2,3).join(" -- ") '
$ echo $(seq 1 10) | tee /dev/stderr |  ruby -lane 'print
$F.values_at(1..5).join(" -- ") '
$ echo $(seq 1 10) | tee /dev/stderr |  ruby -lane 'print
$F.values_at(1,2,3,8,2,2).join(" -- ") '  # posted example
$ head /etc/passwd | tee /dev/stderr |  ruby -F: -lane 'print
$F.values_at(1,2,3,8,2,2).join(" -- ") '
$ head /etc/passwd | tee /dev/stderr |  ruby -F: -lane 'print
$F.values_at(0,2..5).join(" -- ") '
$ head /etc/passwd | tee /dev/stderr |  ruby -F: -lane 'print
$F.values_at(0,2..5).join(" -- ") if $F[2] >= 1000 '
$ head /etc/passwd | tee /dev/stderr |  ruby -F: -lane 'print
$F.values_at(0,2..5).join(" -- ") if $F[2].to_i >= 1000 '
$ cat /etc/passwd | tee /dev/stderr |  ruby -F: -lane 'print
$F.values_at(0,2..5).join(" -- ") if $F[2].to_i >= 1000 '

Regards,
- Robert