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Full Discussion: Avoiding For Loop in Shell Script
Top Forums Shell Programming and Scripting Avoiding For Loop in Shell Script Post 302548589 by hydrabane on Thursday 18th of August 2011 08:45:17 PM
Old 08-18-2011
Avoiding For Loop in Shell Script
I am looking to a solution to the following problem. I have a very large file that looks something like this:

Quote:
0.111 0.111 0.788 0.101 0.800 0.099 0.500 0.255 0.245
0.234 0.675 0.091 0.100 0.088 0.812 0 0 1
Each group of three numbers on each line are three probabilities that sum to one.

I want to output the maximum for each group of three. So desired output would be:

Quote:
0.788 0.800 0.500
0.675 0.812 1
or

Quote:
0.788
0.800
0.500
0.675
0.812
1
I've written the following kludge which works just fine on a small subset of this data but does not scale up well (because it involves an ugly triple nested for loop):

Code:
#!/bin/sh
length=$(awk '{n++}END{print n}' file )
width=$(awk 'NR == 1 { print NF }' file )
width=$( expr $width / 3 )
 
for ((i=1; i <= length; i++))
do
for ((j=1; j <= width; j++))
do
a=$(expr 1 + \( \( $j - 1 \) \* 3 \) )
b=$(expr $a + 2)
awk -v i=$i -v a=$a -v b=$b 'NR == i { for (k = a; k <= b; k++ )if ( $k > max) max = $k } END { print max}' file >> out
done
done

Does anyone know of a solution that will scale up well? Can it be accomplished with basic unix utilities/shell scripting?

Thanks in advance!
 

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lessecho

LESSECHO(1)						      General Commands Manual						       LESSECHO(1)

NAME

       lessecho - expand metacharacters

SYNOPSIS

       lessecho [-ox] [-cx] [-pn] [-dn] [-mx] [-nn] [-ex] [-a] file ...

DESCRIPTION

       lessecho  is  a program that simply echos its arguments on standard output.  But any metacharacter in the output is preceded by an "escape"
       character, which by default is a backslash.

OPTIONS

       A summary of options is included below.

       -ex    Specifies "x", rather than backslash, to be the escape char for metachars.  If x is "-", no escape char is used and  arguments  con-
	      taining metachars are surrounded by quotes instead.

       -ox    Specifies "x", rather than double-quote, to be the open quote character, which is used if the -e- option is specified.

       -cx    Specifies "x" to be the close quote character.

       -pn    Specifies "n" to be the open quote character, as an integer.

       -dn    Specifies "n" to be the close quote character, as an integer.

       -mx    Specifies "x" to be a metachar.  By default, no characters are considered metachars.

       -nn    Specifies "n" to be a metachar, as an integer.

       -fn    Specifies "n" to be the escape char for metachars, as an integer.

       -a     Specifies that all arguments are to be quoted.  The default is that only arguments containing metacharacters are quoted

SEE ALSO

       less(1)

AUTHOR

       This manual page was written by Thomas Schoepf <schoepf@debian.org>, for the Debian GNU/Linux system (but may be used by others).

       Send bug reports or comments to bug-less@gnu.org.

							     Version 487: 25 Oct 2016						       LESSECHO(1)
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