How do I select first string of a two dimensional array to compare to other values?

joi1369 has asked for the wisdom of the Perl Monks concerning the following question:

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Re: How do I select first string of a two dimensional array to compare to other values? by BrowserUk (Patriarch) on Aug 30, 2015 at 23:19 UTC
This: `my $first_value` is not the same variable as this: `print "$first\n";` If you had actually used strict and warnings in your code; they would have told you that. 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. I'm with torvalds on this Agile (and TDD) debunked I told'em LLVM was the way to go. But did they listen!	[reply] [d/l] [select]
Re^2: How do I select first string of a two dimensional array to compare to other values? by joi1369 (Initiate) on Aug 31, 2015 at 00:54 UTC
That was completely my fault. I was trying to clarify once I had put it on the site and then ended up forgetting to change the other one.	[reply]
Re: How do I select first string of a two dimensional array to compare to other values? by choroba (Cardinal) on Aug 30, 2015 at 23:17 UTC
Hi joi1369, welcome to the Monastery! I don't understand your question. It's usually better to include sample input data (within `<code>` tags) and expected output. If you want to work with the first line only, don't use `while`. If you want to compare two string values, you should use `eq`, `ne`, or `index`, or maybe a regex: `$value =~ /\Q$important/`. Update: example script added: `#!/usr/bin/perl use warnings; use strict; my $first_line = <DATA>; my $important = (split ' ', $first_line)[0]; while (<DATA>) { # Process the remaining lines. my $value = (split)[0]; print if $value eq $important; } __DATA__ john chevrolet usa hans bmw germany ivan lada russia john talbot uk` [download] لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l] [select]
Re^2: How do I select first string of a two dimensional array to compare to other values? by joi1369 (Initiate) on Aug 31, 2015 at 01:05 UTC
Thank you for the welcome! Let me try to clarify things a bit. This is the input- `1424621700, 2015-02-22 16:15:00, 4294.700 1424621760, 2015-02-22 16:16:00, 4289.700 1424621820, 2015-02-22 16:17:00, 4299.800 1424621880, 2015-02-22 16:18:00, 4302.800 1424621940, 2015-02-22 16:19:00, 4296.900 1424622000, 2015-02-22 16:20:00, 4301.000` [download] I'm trying to run it through this script (fixed from above)- `#!/usr/bin/perl use strict; use warnings; my $file = $ARGV[0]; open (RAW, "./$file") or die "Can't open $file for read: $!"; open (OUT, ">./OUTPUT_$file") or die "Can't open Output_$file: $!"; while(<RAW>) { my $line = $_; chop($line); next if ($line =~ /!/); my @splits = split (',', $line); my $first_line = $splits; print "$first_line\n"; }` [download] I am trying to get the string "1424621700" assigned to "$first_line" and then printed. Sorry about the disorganization. I'm new to Perl and haven't quite gotten the hang of it yet.	[reply] [d/l] [select]
Re^3: How do I select first string of a two dimensional array to compare to other values? by AnomalousMonk (Archbishop) on Aug 31, 2015 at 01:11 UTC
So how does your current code fail to serve your purposes? An alternative: `c:\@Work\Perl\monks>perl -wMstrict -le "my $line = qq{1424621700, 2015-02-22 16:15:00, 4294.700\n}; chomp $line; print qq{'$line'}; ;; my ($first) = split m{ , \s* }xms, $line; print qq{'$first'}; " '1424621700, 2015-02-22 16:15:00, 4294.700' '1424621700'` [download] Update: Ah, I see it now: `my $first_line = $splits;` and again, how can this compile with strict enabled? You probably want something like the `my $first_line = $splits[0];` statement you had before. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^4: How do I select first string of a two dimensional array to compare to other values? by joi1369 (Initiate) on Aug 31, 2015 at 01:19 UTC
Re^5: How do I select first string of a two dimensional array to compare to other values? by AnomalousMonk (Archbishop) on Aug 31, 2015 at 01:49 UTC
Re^5: How do I select first string of a two dimensional array to compare to other values? by AnomalousMonk (Archbishop) on Aug 31, 2015 at 01:30 UTC
Re: How do I select first string of a two dimensional array to compare to other values? by AnomalousMonk (Archbishop) on Aug 30, 2015 at 23:30 UTC
I have a two dimensional array after splitting a text document into three different columns. You split with `my @splits = split (',', $line);` to the array `@splits` which has one dimension. On what do you base your assertion that you have a two-dimensional array? You assign the first element of `@splits` to `$first_value` and then print `$first` (which is never defined) immediately afterward. How ~~does~~ \| can that work with strict enabled? Can you supply a short, representative example or two of your input data? We could then use this for testing various alternatives. Also, please see the Short, Self Contained, Correct (Compilable), Example discussion. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^2: How do I select first string of a two dimensional array to compare to other values? by joi1369 (Initiate) on Aug 31, 2015 at 00:58 UTC
I said this above as well but, the non-defined "$first" was completely my fault. I was trying to clarify the code a bit once I had put it on the site and then ended up forgetting to change the other one. The input looks like this- `1424621700, 2015-02-22 16:15:00, 4294.700 1424621760, 2015-02-22 16:16:00, 4289.700 1424621820, 2015-02-22 16:17:00, 4299.800 1424621880, 2015-02-22 16:18:00, 4302.800 1424621940, 2015-02-22 16:19:00, 4296.900 1424622000, 2015-02-22 16:20:00, 4301.000` [download] And I'm trying to get the value "1424621700" returned after the file is split at the commas.	[reply] [d/l]
Re^3: How do I select first string of a two dimensional array to compare to other values? by AnomalousMonk (Archbishop) on Aug 31, 2015 at 01:17 UTC
Please see above. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l]
Re: How do I select first string of a two dimensional array to compare to other values? by 1nickt (Canon) on Aug 31, 2015 at 05:41 UTC
`#!/usr/bin/perl use strict; use warnings; use feature qw/ say /; my $first = ( split ',', <DATA> )[0]; say $first; __DATA__ 1424621700, 2015-02-22 16:15:00, 4294.700 1424621760, 2015-02-22 16:16:00, 4289.700 1424621820, 2015-02-22 16:17:00, 4299.800 1424621880, 2015-02-22 16:18:00, 4302.800 1424621940, 2015-02-22 16:19:00, 4296.900 1424622000, 2015-02-22 16:20:00, 4301.000 1424622060, 2015-02-22 16:21:00, 4300.300` [download] $ perl 1140499.pl 1424621700 $ [download] ++james28909 for making me see it more simply. The way forward always starts with a minimal test.	[reply] [d/l] [select]
Re: How do I select first string of a two dimensional array to compare to other values? by 1nickt (Canon) on Aug 31, 2015 at 01:42 UTC
Hi there, it looks like you want to do this: `#!/usr/bin/perl use strict; use warnings; my $file = '1140475.txt';; open my $raw, '<', $file or die "open: $!"; open my $out, '>', "out_$file" or die "close: $!"; while ( my $line = <$raw> ) { chomp( $line ); my @splits = split ( ',', $line ); print $out "First line, first field: $splits[0]\n"; last; } close $out or die "close: $!"; __END__` [download] Output: `$ cat out_1140475.txt First line, first field: 1424621700` [download] But you should use a module if you can. A lot of people like Path::Tiny because it does the file opening, reading, and chomping, for you. In the example below I use `split()` on the first element of the array of lines returned by `Path::Tiny::path()` (there's actually only one line since I set the 'count' attribute), and then I assign the first element of the result of `split()` to `$first`. `#!/usr/bin/perl use strict; use warnings; use Path::Tiny qw/ path /; my $file = '1140475.txt'; my $first = ( split ',', (path($file)->lines( {chomp => 1, count => 1} + ))[0] )[0]; print "$first\n"; __END__` [download] Output: $ perl 1140475-2.pl 1424621700 $ [download] Hope this helps! The way forward always starts with a minimal test.	[reply] [d/l] [select]
Re: How do I select first string of a two dimensional array to compare to other values? by AnomalousMonk (Archbishop) on Aug 31, 2015 at 01:38 UTC
BTW: Your OP was changed to add some example data. The conventional practice of this site is to also add a note to any altered node to indicate what was changed or deleted. Please see How do I change/delete my post?. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l]
Re: How do I select first string of a two dimensional array to compare to other values? by james28909 (Deacon) on Aug 31, 2015 at 05:13 UTC
`use strict; use warnings; print $_ for my ($data) = split ',', <DATA>; __DATA__ 123,456 234,567 345,456 #outputs: '123'` [download]	[reply] [d/l]
Re^2: How do I select first string of a two dimensional array to compare to other values? by 2teez (Vicar) on Aug 31, 2015 at 06:25 UTC
hi james28909, if split operator can take a regex, why not just: `use strict; use warnings; print split /,.+/, <DATA>; __DATA__ 123,456 234,567 345,456` [download] Just a flash of thought! :) If you tell me, I'll forget. If you show me, I'll remember. if you involve me, I'll understand. --- Author unknown to me	[reply] [d/l]
Re: How do I select first string of a two dimensional array to compare to other values? by poj (Abbot) on Aug 31, 2015 at 09:12 UTC
Here is an example using the first line of data compared to the other values. Note, it skips lines containing ! which may precede the first data line #!/usr/bin/perl use strict; use warnings; my $file = $ARGV[0]; open (RAW, '<', "./$file") or die "Can't open $file for read: $!"; my @first; my $line_count = 0; while (<RAW>){ chomp; next if /!/; my @col = split /,/,$_; if (++$line_count == 1){ @first = @col; print "\n--------------------------------\n"; print "Start $first[1]\n"; print sprintf "%10s %10s %10s\n",'+secs','value','change'; print sprintf "%10s %10s %10s\n",'-'x10,'-'x10,'-'x10; } print sprintf "%10d %10.3f %10.3f\n", ($col[0] - $first[0]), $col[2], ($col[2] - $first[2]); } [download] Outputs `-------------------------------- Start 2015-02-22 16:15:00 +secs value change ---------- ---------- ---------- 0 4294.700 0.000 60 4289.700 -5.000 120 4299.800 5.100 180 4302.800 8.100 240 4296.900 2.200 300 4301.000 6.300 360 4300.300 5.600` [download] poj	[reply] [d/l] [select]
Re: How do I select first string of a two dimensional array to compare to other values? by sundialsvc4 (Abbot) on Aug 31, 2015 at 01:34 UTC
It certainly looks to me that the `print` statement is within the `while` loop, such that it will print every value retrieved from the file-handle. You do need the loop, presumably, because you have a `next if` test to exclude certain lines. But, once you reach the point where the `print` statement is now located, you probably (instead ...) want to use a `last` statement to force a premature end to the while-loop: the first value is now in `$first_value`, and you do not wish to continue reading. After the `}` symbol which ends the while-loop, you can, if you like, put the `print` statement to see it. If, later on in the program, you start another `while` loop using the same file-handle, it should resume reading the file where it left off. (Unless you use `fseek()` to reposition it.) - - - (In the future, it will help us considerably if you’ll routinely tell us more information: a snippet of what the file looks like, and a brief description of what output you are seeing and why you feel that the output is wrong.) Meanwhile, Welcome to the Monastery!!


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