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Top Forums Shell Programming and Scripting Find Where Values Change From Positive To Negative and viceversa Post 302503775 by malandisa on Friday 11th of March 2011 03:44:49 PM
Old 03-11-2011
Find Where Values Change From Positive To Negative and viceversa

Hi all,

I have a file that looks like shown below. I want to find places where the value in column 2 change from negative to positive and vice versa and return the value on column 1 at that point. I wonder if this is possible in shell script or awk .. please help!

Here is the original data

Quote:
2.91 -1.19 1.34 78.00 2.00
3.09 -1.21 1.33 91.00 2.00
3.28 -1.03 1.41 87.00 2.00
3.47 -0.78 1.48 86.00 2.00
3.66 -0.47 1.51 86.00 2.00
3.84 0.01 1.42 88.00 2.00
4.03 0.47 1.15 85.00 2.00
4.22 0.93 0.45 87.00 2.00
4.41 1.00 0.00 87.00 1.00
4.59 1.00 0.00 87.00 1.00
4.78 1.00 0.00 87.00 1.00
4.97 1.00 0.00 84.00 1.00
5.16 1.00 0.00 88.00 1.00
5.34 1.00 0.00 86.00 1.00
8.53 1.00 0.00 86.00 1.00
8.72 1.00 0.00 87.00 1.00
8.91 1.00 0.00 78.00 1.00
9.09 1.00 0.00 91.00 1.00
9.28 1.00 0.00 87.00 1.00
9.47 1.00 0.00 86.00 1.00
9.66 1.00 0.00 86.00 1.00
9.84 1.00 0.00 88.00 1.00
10.03 0.54 1.09 85.00 2.00
10.22 -0.86 1.46 87.00 2.00
10.41 -1.86 0.63 87.00 2.00
10.59 -1.76 0.82 87.00 2.00
10.78 -0.83 1.47 87.00 2.00
10.97 0.07 1.40 84.00 2.00
11.16 0.80 0.76 88.00 2.00
11.34 1.00 0.00 86.00 1.00
And the desired output is

Quote:
3.66
10.03
10.78
Is there a way I can do this? And sorry I am a real newbie in shell scripting and I have no clue how to start this and so I have no suggested code

Thank you very much for your assistance and advice
Malandisa
 

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SHELL-QUOTE(1)						User Contributed Perl Documentation					    SHELL-QUOTE(1)

NAME
shell-quote - quote arguments for safe use, unmodified in a shell command SYNOPSIS
shell-quote [switch]... arg... DESCRIPTION
shell-quote lets you pass arbitrary strings through the shell so that they won't be changed by the shell. This lets you process commands or files with embedded white space or shell globbing characters safely. Here are a few examples. EXAMPLES
ssh preserving args When running a remote command with ssh, ssh doesn't preserve the separate arguments it receives. It just joins them with spaces and passes them to "$SHELL -c". This doesn't work as intended: ssh host touch 'hi there' # fails It creates 2 files, hi and there. Instead, do this: cmd=`shell-quote touch 'hi there'` ssh host "$cmd" This gives you just 1 file, hi there. process find output It's not ordinarily possible to process an arbitrary list of files output by find with a shell script. Anything you put in $IFS to split up the output could legitimately be in a file's name. Here's how you can do it using shell-quote: eval set -- `find -type f -print0 | xargs -0 shell-quote --` debug shell scripts shell-quote is better than echo for debugging shell scripts. debug() { [ -z "$debug" ] || shell-quote "debug:" "$@" } With echo you can't tell the difference between "debug 'foo bar'" and "debug foo bar", but with shell-quote you can. save a command for later shell-quote can be used to build up a shell command to run later. Say you want the user to be able to give you switches for a command you're going to run. If you don't want the switches to be re-evaluated by the shell (which is usually a good idea, else there are things the user can't pass through), you can do something like this: user_switches= while [ $# != 0 ] do case x$1 in x--pass-through) [ $# -gt 1 ] || die "need an argument for $1" user_switches="$user_switches "`shell-quote -- "$2"` shift;; # process other switches esac shift done # later eval "shell-quote some-command $user_switches my args" OPTIONS
--debug Turn debugging on. --help Show the usage message and die. --version Show the version number and exit. AVAILABILITY
The code is licensed under the GNU GPL. Check http://www.argon.org/~roderick/ or CPAN for updated versions. AUTHOR
Roderick Schertler <roderick@argon.org> perl v5.16.3 2010-06-11 SHELL-QUOTE(1)
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