shell script for matrix operation

dynamics · 09-17-2010, 06:09 AM

I have 3 files and each contain m*n matrix.
m = number of rows (horizontal lines)
n = number of columns (entries in a particular line)

What I wish to find is the sum of the 2nd number in the last row.
Ex

file1.dat

2 5 8 8
4 6 7 8
3 8 3 7

file2.dat
3 4 1 4
8 4 0 3
4 7 3 7

file3.dat
9 6 3 5
8 4 8 4
7 5 6 8

The desired result is 8+7+5 ie., 20

Thanks in advance for the help. A little bit of explanation about how the script works will be very helpful.

jrosco · 09-17-2010, 09:28 AM

There might be better way to do this, but what springs to mind would something like

Code:

file1=$(tail -n 1 /tmp/file1.dat); file1=$(echo ${file1:1:1})

file2=$(tail -n 1 /tmp/file2.dat); file2=$(echo ${file2:1:1})

file3=$(tail -n 1 /tmp/file3.dat); file3=$(echo ${file3:1:1})

result=$(expr $file1 + $file2 + $file3)

echo $result

tail -n 1 file #would get the last line of a file

echo ${var:1:1} #would extract characters at position:length var is the string, the first 1 is the position and the second 1 is the length.

Like I said there could be a better way to do this.

JC

kurumi · 09-17-2010, 09:43 AM

Code:

ruby -e 't=0;ARGV.each{|x| t+=IO.readlines(x).last.split[1].to_i};puts "total: #{t}"' file1 file2 file3

dynamics · 09-17-2010, 11:00 AM

Quote:

Originally Posted by jrosco

There might be better way to do this, but what springs to mind would something like

Code:

file1=$(tail -n 1 /tmp/file1.dat); file1=$(echo ${file1:1:1})

file2=$(tail -n 1 /tmp/file2.dat); file2=$(echo ${file2:1:1})

file3=$(tail -n 1 /tmp/file3.dat); file3=$(echo ${file3:1:1})

result=$(expr $file1 + $file2 + $file3)

echo $result

tail -n 1 file #would get the last line of a file

echo ${var:1:1} #would extract characters at position:length var is the string, the first 1 is the position and the second 1 is the length.

Like I said there could be a better way to do this.

JC

Hi JC
The solution works if my matrix entry are single digits. If they are floating point numbers then the above method does not seems to be working.
Thanks

quanta · 09-17-2010, 11:13 AM

Quote:

Originally Posted by dynamics

Hi JC
The solution works if my matrix entry are single digits. If they are floating point numbers then the above method does not seems to be working.
Thanks

Change to:

Code:

result=`echo "($file1 + $file2 + $file3)" | bc`

jrosco · 09-18-2010, 09:31 PM

Didn't realize before, but does the file contain spaces between the characters?

JC

grail · 09-19-2010, 08:34 PM

awk would work:

Code:

awk 'FNR==3{sum+=$2}END{print sum}' file*.dat

awk is able to do floating point too