Access and modify specific element of tab delimited .txt file

K_Edw has asked for the wisdom of the Perl Monks concerning the following question:

Given a matrix stored as a tab-delimited file with row + col headers, the upper left entry is often blank (a single tab):

    A    B    C    D    E
A    1    1    1    1    1
B    1    1    1    1    1
C    1    1    1    1    1
D    1    1    1    1    1
E    1    1    1    1    1
[download]

I wish to be able to access and modify this entry. Ordinarily to access a specific element I would use something like:

perl -lanse 'print $F[$j-1] if $. == $i' -- -i=1 -j=1

However this prints 'A' and does not recognise the initial tab as counting as an element. Is there a way to print something into this first element? For example producing:

ID    A    B    C    D    E
A    1    1    1    1    1
B    1    1    1    1    1
C    1    1    1    1    1
D    1    1    1    1    1
E    1    1    1    1    1
[download]

Comment on Access and modify specific element of tab delimited .txt file Select or Download Code

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Re: Access and modify specific element of tab delimited .txt file by Eily (Monsignor) on Mar 30, 2016 at 11:21 UTC
You can use the -F option to specify the split pattern for each line. If the pattern is found at the beginning of the string, $F[0] will be the empty string. Edit: so replacing the empty element with 'ID' can be done like this: `perl -lF"\t" -E 'print join qq<\t>, map { $_ \|\| q<ID> } @F'`, which works because there are no 0 in your values.	[reply] [d/l]
Re: Access and modify specific element of tab delimited .txt file by BrowserUk (Patriarch) on Mar 30, 2016 at 11:16 UTC
Is there a way to print something into this first element? I suspect you're after something more complex, but on the face of it, this seems to answer that question: `C:\test>type junk.dat A B C D E A 1 1 1 1 1 B 1 1 1 1 1 C 1 1 1 1 1 D 1 1 1 1 1 E 1 1 1 1 1 C:\test>perl -plae" $.== 1 and $F[0] eq 'A' and $_ = 'ID' . $_" junk.d +at ID A B C D E A 1 1 1 1 1 B 1 1 1 1 1 C 1 1 1 1 1 D 1 1 1 1 1 E 1 1 1 1 1` [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I knew I was on the right track :) In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]
Re^2: Access and modify specific element of tab delimited .txt file by K_Edw (Beadle) on Mar 30, 2016 at 12:24 UTC
Thanks! This works well (after replacing " with '). It is slightly more complex in that $F[0] will not always eq 'A', so this could also be used: `perl -plae '$.== 1 and $_ = 'ID' . $_'`	[reply] [d/l]
Re^3: Access and modify specific element of tab delimited .txt file by BrowserUk (Patriarch) on Mar 30, 2016 at 12:32 UTC
Is there a way for it to simply check for any string (non-delimiter character) at all? Eily called it right: `C:\test>type junk.dat A B C D E A 1 1 1 1 1 B 1 1 1 1 1 C 1 1 1 1 1 D 1 1 1 1 1 E 1 1 1 1 1 C:\test>perl -F\t -plae"$.== 1 and $F[0] eq '' and $_ = 'ID' . $_" jun +k.dat ID A B C D E A 1 1 1 1 1 B 1 1 1 1 1 C 1 1 1 1 1 D 1 1 1 1 1 E 1 1 1 1 1` [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I knew I was on the right track :) In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]
Re: Access and modify specific element of tab delimited .txt file by duelafn (Parson) on Mar 30, 2016 at 14:05 UTC
If you literally only need to create first entry, don't split? `perl -pe 'BEGIN { print "ID"; }' /tmp/test.dat` [download] Good Day, Dean	[reply] [d/l]
Re^2: Access and modify specific element of tab delimited .txt file by mr_mischief (Monsignor) on Mar 31, 2016 at 15:19 UTC
This is an excellent example of finding the X in an X/Y problem. You've done a good job of separating the problem from the proposed solution on even a fairly simple example program. I'm going to bookmark this to reference for future discussions of this sort.	[reply]