Adding a column to a text based on file name

rlapate · #1 (**permalink**) 05-23-2009

Dear all,

Does anyone know how I could to add a column of numbers (1s, or 2s, or..., or 6s) to two-column text files (tab-delimited), where the specific number to be added varies as a function of the file naming?

Currently, each of my text files has two columns, so the column with the repeated number in it would be the third column. The groups of six text files are located within separate directories, and the easiest way to get at their naming (which determines which number should be added) is by using "ls" - it will always list them in the right order, such that first text file listed should have a third column added with "1s" (for as many rows as it has; where the number of rows varies depending on the specific text file); and the second text file listed should have a third column appended with "2s", so on and so forth.

I am still quite new to programming, and my intuition tells me I should use the command "ls" and then pipe "|" that to a certain command that would execute "if the file is the first one, add a column of ones, if file is the second one, a column of twos..." etc.

Thank you so much for any feedback!

Regina

vidyadhar85 · #2 (**permalink**) 05-23-2009

what have you tried till now??

cfajohnson · #3 (**permalink**) 05-23-2009

Quote:

Originally Posted by rlapate

Dear all,

Does anyone know how I could to add a column of numbers (1s, or 2s, or..., or 6s) to two-column text files (tab-delimited), where the specific number to be added varies as a function of the file naming?

Currently, each of my text files has two columns, so the column with the repeated number in it would be the third column. The groups of six text files are located within separate directories, and the easiest way to get at their naming (which determines which number should be added) is by using "ls" - it will always list them in the right order, such that first text file listed should have a third column added with "1s" (for as many rows as it has; where the number of rows varies depending on the specific text file); and the second text file listed should have a third column appended with "2s", so on and so forth.

You don't need ls for that; in fact, it's usually the wrong way to do it. Use filename expansion instead.

Quote:

I am still quite new to programming, and my intuition tells me I should use the command "ls" and then pipe "|" that to a certain command that would execute "if the file is the first one, add a column of ones, if file is the second one, a column of twos..." etc.

No, loop through the files with filename expansion.
Code:
n=1
for file in [whatever pattern works]
do
  awk -v num=$n '{ $(NF+1) = num; print }' "$file" > "$file.new"
  n=$(( $n + 1 ))
done
The awk script might have to be tweaked, depending on the exact format of the files.

devtakh · #4 (**permalink**) 05-23-2009

You might want to do something like

Code:

 i=1;
for file in *.txt; 
do 
awk -F "\t" -v n=$i '{print $0,n}' OFS="\t" $file > $file.tmp;
mv $file.tmp $file; 
i=`expr $i \+ 1 `
done

-Devaraj Takhellambam

cfajohnson · #5 (**permalink**) 05-23-2009

Quote:

Originally Posted by devtakh

You might want to do something like

Code:

i=`expr $i \+ 1 `

You don't want to use an external command for simple arithmetic:
Code:
i=$(( $i + 1 ))

vidyadhar85 · #6 (**permalink**) 05-23-2009

Quote:

Originally Posted by cfajohnson

You don't want to use an external command for simple arithmetic:
Code:
i=$(( $i + 1 ))

you don't wanna use extra "$" inside

Code:

 
i=$((i+1))

cfajohnson · #7 (**permalink**) 05-23-2009

Quote:

Originally Posted by vidyadhar85

you don't wanna use extra "$" inside

Code:

 
i=$((i+1))

Yes I do. I want my code to be legible.

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