Hey,
Pretty awesome site you've got here (spent most of my morning on it!).
I am new to Perl (or any sort of data lengua for that matter), currently in chapter 10 of the lama. I am trying to get my perl program to focus only on one column (C) in my data set and from searching your site I thought that maybe something simple as referring to it as "colC" would cut it... but it is not working.
As I said, I am new to this and if this is a completely rudementary question - I do appologize!

I have attached my program below, and I hope you will take the time to look it over.
Thanks,
Heidi


#!/usr/bin/perl/
use warnings;
#---------------------------------------
# Need to:
# put program and files to be include into the same folder,
# on the command page print the name of this program;
#---------------------------------------
# Objective:
#  to make the program pick out only one column in the csv data file,
#  disregard the header line, and count the number of times a number shows up.


print "Make sure all your files are in the same folder as this program. print the name of your first file to be included.\n";
chomp (my $file1 = <STDIN>);


open VRFILE, "$file1";

Code: $file1=',';

my @data= $colC;             # get the column of data from column c (what about the header?)
my %count;                   # creating a new hash to use for count of each id number
$count{$_}++ foreach @data;  #creates the new keys and values

print %count;

close VRFILE;



You appear to be missing some very fundamental concepts, did you read all the chapters up to 10 or are you skipping chapters? If it is a very simple CSV file you would use the split() function to parse each line into its columns.  

Thanks Kevin...  I did indeed read all the chapters, didn't skip a single paragraph. However, since this book is the first introduction I have had to any sort of computer stuff there is bound to be stuff that I haven't gotten a hold on yet - despite intensive use of websources to find out definitions of multiple "x-names".
As I said, I was aware that my question might be too simple.
Heidi

Trying to manually parse a CSV file can be a bad idea, but if it is a simple CSV file the general idea is:


open (FH, 'yourcsvfile') or die "$!";
while(<FH>){
  my $colc = (split(/,/))[2];
  print $colc,"\n";
}
close FH:

assumes column C is the third column in a line, something like:

12,34,56,78,90

where 56 is column C.

Thanks Kevin,
I will give that a whirl!
I would consider the csv file simple in that it is automatically generated with "natural columns" but the file is rather large so I am wondering why you are saying that it can be a bad idea.
Also, do you know of any tutorial or book that emphasises data management/extraction that you could refer me to?
Thanks again!


on 05/30/08 at 17:20:47, Heidi wrote:

Thanks Kevin, I will give that a whirl! I would consider the csv file simple in that it is automatically generated with "natural columns" but the file is rather large so I am wondering why you are saying that it can be a bad idea. Also, do you know of any tutorial or book that emphasises data management/extraction that you could refer me to? Thanks again!

Parsing a CSV file is really a bit tricky, doing it manually can lead to problems. I recommend you look into Text::CSV_XS to pase CSV files:

http://search.cpan.org/~hmbrand/Text-CSV_XS-0.45/CSV_XS.pm

Data management ( a very wide open topic )  is not one of my strong points, but there is a good book, if a little old now, written by Dave Cross (long time perl developer and contributor): Data Munging

http://www.manning.com/cross/





Hi Kevin,

I have a csv file(1) with time (Gmt) m/d/yr hr:min in column A.

A csv file(2) with time (Gmt) hr:min in column A (start) and column B (end) (these are all the same date which is provided else where)

I need to get the time interval between file(2) column A and B, use that to extract the data from within file(1) column C with corresponding times (file(1)columnA).
Any suggestions?

How do I use the "$time = timegm" function?

Thanks


There's a example of timelocal at
http://www.wellho.net/resources/ex.php4?item=p216/tim
- just replace local with gm in the call.

Note also down the right hand side of that page there are links to a few other date and time functions.

Seriously - so many people have written time and date handlers for Perl that there was a joke that there was a module for every day of the month!

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