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How to subtract the adjacent lines from a single column?

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# 1  
Old 02-23-2010
How to subtract the adjacent lines from a single column?
Hi All,

I have a file with only one column and i need to subtract the adjacent lines of the same column and print it in the same column.

For Example:
(Input)
HTML Code:
Col1

5
10
12
6
9
12
5
.
.
.
.
output should be like this:
HTML Code:
Col1

5
2
-6
3
3
-7
.
.
.
.
Can anyone help me in this regard?

Expecting your reply and Thanks in advance.

Warm regards
Fredrick.
# 2  
Old 02-23-2010
Try this:

Code:
awk 'p{print $0-p}{p=$0}' file


As always, we also appreciate any reaction from the Original Poster after an answer, thank you.
Last edited by Franklin52; 02-23-2010 at 09:29 AM..
# 3  
Old 02-23-2010
Frank, Can you please brief how this awk code works?
# 4  
Old 02-23-2010
One in perl..

Code:
perl -e '@A=<>; while (++$i <=$#A ) { print $A[$i]-$A[$i-1],"\n"; }' file

For frankin's snippet,

Code:
awk 'p{print $0-p}{p=$0}' file

For the first time, as p will be valuated as FALSE and will not execute {print $0-p}. However, p will turn to a non-zero/TRUE value when it execute {p=$0}.From second record onwards, p will be TRUE and will evaluate {print $0-p} and print it.Also, it will set the new value(current line) to p
Last edited by dennis.jacob; 02-23-2010 at 12:51 PM..
# 5  
Old 02-23-2010
I got it. Thanks Dennis.
# 6  
Old 02-23-2010
Franklin52's solution is probably the best, simplest, and shortest there is. However, that shouldn't stop unix userland lovers from having some fun Smilie

Code:
sed 'x;G;1d;y/\n/+/;s/.*/eval(-&)/' data | m4

Only works with integers, as opposed to the AWK which will handle floating point as well, and assumes that the data file consists of nothing but one integer per line.

Code:
$ cat data
5
10
12
6
9
12
5

$ sed 'x;G;1d;y/\n/+/;s/.*/eval(-&)/' data | m4
5
2
-6
3
3
-7

Cheers,
Alister
# 7  
Old 02-23-2010
Quote:
Originally Posted by Franklin52
Try this:

Code:
awk 'p{print $0-p}{p=$0}' file


As always, we also appreciate any reaction from the Original Poster after an answer, thank you.
If we have zero in input file then we will not get the difference.

Code:
awk 'NR-1{print $0-p}{p=$0}' file
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