[30108] in Perl-Users-Digest
Perl-Users Digest, Issue: 1351 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Mon Mar 10 16:20:07 2008
Date: Mon, 10 Mar 2008 13:19:58 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Mon, 10 Mar 2008 Volume: 11 Number: 1351
Today's topics:
Updating single array element seems to send array out o <ed.whyatt@gmail.com>
Re: Updating single array element seems to send array o <ed.whyatt@gmail.com>
Re: Updating single array element seems to send array o <someone@example.com>
Re: Updating single array element seems to send array o <someone@example.com>
Re: Updating single array element seems to send array o <m@rtij.nl.invlalid>
Re: Use of "return" in place of "last" (newbie question <tzz@lifelogs.com>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Mon, 10 Mar 2008 07:41:03 -0700 (PDT)
From: whyatt <ed.whyatt@gmail.com>
Subject: Updating single array element seems to send array out of kilter.
Message-Id: <0600edf3-b719-4247-a704-a40d42aefb4e@n75g2000hsh.googlegroups.com>
Hi all,
Forgive me for my perl inadequacies, but hopefully it is a very simple
solution that I am striving for.
The pseudocode of what I am attempting to do is as follows:
1. Read contents of a file and parse data into 2 arrays - person and
count.
2. Print out status of current arrays
3. Randomly choose one person from array 1 and increment the count by
1, updating the associated array element.
4. Print out new status of arrays.
The issue I face is that the print in task 2 nicely places each entry
on a single line, with no use of "\n".
After running task 3, the print in task 4 no longer places each entry
on a single line, rather causes lines to merge. I've scratched my head
for a day on this now, trying various different things with no luck.
Perhaps someone in this group can check my code and advise. (The input
file is a comma separated list)
Thanks in advance,
Ed
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++
sub getsendersfile
{
my $sendersfile = "icc_senders.csv";
open(FILEHANDLE, $sendersfile) || die "Cannot open file. $!";
until (eof FILEHANDLE)
{
return @allsenders = <FILEHANDLE>;
}
close FILEHANDLE;
}
sub readsendersfile
{
@senderslist = ();
@senderslistcount = ();
for (my $count = 0; $count <= $#allsenders ; $count++)
{
$senderslist[$count] = ((split ",",$allsenders[$count])[0]);
$senderslistcount[$count] = ((split ",",$allsenders[$count])[1]);
print "$count : $senderslist[$count] : $senderslistcount[$count]";
}
print "\n";
$numemp = $#senderslist + 1;
print "$numemp\n";
}
sub choosesender
{
foreach (1..10)
{
#pick random sender
my @sender = ();
my $sendernumber = (int rand($numemp));
$sender[0] = $senderslist[$sendernumber];
my $newcount = $senderslistcount[$sendernumber];
$newcount = ($newcount+1);
splice @senderslistcount,$sendernumber,1,$newcount;
}
for (my $count = 0; $count <= $#allsenders ; $count++)
{
print "$count : $senderslist[$count] : $senderslistcount[$count]";
}
}
getsendersfile();
readsendersfile();
choosesender();
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++
Results in my tests:
0 : tremlett@whyatt.local : 0
1 : anderson@whyatt.local : 0
2 : vaas@whyatt.local : 0
3 : aadams@whyatt.local : 0
4 : marshall@whyatt.local : 0
5 : iqbal@whyatt.local : 0
6 : gibbs@whyatt.local : 0
7 : maharoof@whyatt.local : 0
8 : mason@whyatt.local : 0
9 : langeveldt@whyatt.local : 0
10 : rehman@whyatt.local : 0
11 : lokuhettige@whyatt.local : 0
12 : cook@whyatt.local : 0
13 : panesar@whyatt.local : 0
14 : boucher@whyatt.local : 0
15 : chandana@whyatt.local : 0
16 : atapattu@whyatt.local : 0
17 : kallis@whyatt.local : 0
18 : jayasuriya@whyatt.local : 0
19 : collymore@whyatt.local : 0
20
0 : tremlett@whyatt.local : 11 : anderson@whyatt.local : 12 :
vaas@whyatt.local : 0
3 : aadams@whyatt.local : 0
4 : marshall@whyatt.local : 0
5 : iqbal@whyatt.local : 16 : gibbs@whyatt.local : 17 :
maharoof@whyatt.local : 0
8 : mason@whyatt.local : 0
9 : langeveldt@whyatt.local : 0
10 : rehman@whyatt.local : 111 : lokuhettige@whyatt.local : 112 :
cook@whyatt.local : 113 : panesar@whyatt.local : 0
14 : boucher@whyatt.local : 115 : chandana@whyatt.local : 116 :
atapattu@whyatt.local : 0
17 : kallis@whyatt.local : 0
18 : jayasuriya@whyatt.local : 0
19 : collymore@whyatt.local : 1
------------------------------
Date: Mon, 10 Mar 2008 09:10:21 -0700 (PDT)
From: whyatt <ed.whyatt@gmail.com>
Subject: Re: Updating single array element seems to send array out of kilter.
Message-Id: <60dc17ed-621b-498d-8a9a-b5d74317d387@m36g2000hse.googlegroups.com>
On 10 Mar, 15:35, Martijn Lievaart <m...@rtij.nl.invlalid> wrote:
> On Mon, 10 Mar 2008 07:41:03 -0700, whyatt wrote:
> > Hi all,
>
> > Forgive me for my perl inadequacies, but hopefully it is a very simple
> > solution that I am striving for.
>
> > The pseudocode of what I am attempting to do is as follows: 1. Read
> > contents of a file and parse data into 2 arrays - person and count.
> > 2. Print out status of current arrays 3. Randomly choose one person from
> > array 1 and increment the count by 1, updating the associated array
> > element. 4. Print out new status of arrays.
>
> > The issue I face is that the print in task 2 nicely places each entry on
> > a single line, with no use of "\n".
>
> Which is strange at first, where does the newline come from? It's tagged
> on to the count, because you don't chomp your input.
>
>
>
> > After running task 3, the print in task 4 no longer places each entry on
> > a single line, rather causes lines to merge. I've scratched my head for
> > a day on this now, trying various different things with no luck. Perhaps
> > someone in this group can check my code and advise. (The input file is a
> > comma separated list)
>
> You should have:
> - Posted (a small sample of) the inputfile
> - Posted a complete program, not hust the snipped you have trouble with.
>
> Without a complete program, it is difficult to check. Some random
> comments:
>
>
>
> > sub getsendersfile
> > {
> > my $sendersfile = "icc_senders.csv";
> > open(FILEHANDLE, $sendersfile) || die "Cannot open file. $!";
>
> Better use lexical filehandles.
>
> open(my $fh, $sendersfile) or die "Cannot open '$sendersfile' for
> reading. $!";
>
> > until (eof FILEHANDLE)
> > {
> > return @allsenders = <FILEHANDLE>;
> > }
> > close FILEHANDLE;
> > }
>
> This is nonsense, return, returns, so the loop is eecuted exactly once.
>
> Replace with:
>
> # use a temporary to force list context
> my @t = <FILEHANDLE>
> return chomp(@t);
>
> However, you seem to set the global @allsenders as well. So what is the
> use of returning something?
>
>
>
> > sub readsendersfile
>
> This sub does not *read* the file, it parses it. So the name is
> misleading.
>
> > {
> > @senderslist = ();
> > @senderslistcount = ();
>
> Are these globals or locals? This part smells wrong.
>
> > for (my $count = 0; $count <= $#allsenders ; $count++) {
>
> This is a C style loop, Perl has more effective mechanisms.
>
>
>
> > $senderslist[$count] = ((split ",",$allsenders[$count])
> [0]);
> > $senderslistcount[$count] = ((split ",",$allsenders
> [$count])[1]);
> > print "$count : $senderslist[$count] : $senderslistcount
> [$count]";
> > }
>
> my %count;
> for (@allsenders) {
> my ($email, $cnt) = split(/,/);
> $count{$email} = $cnt;
> print "$email: $cnt\n";
> }
>
> You loose the numbering, but do you really need that?
>
> > print "\n";
> > $numemp = $#senderslist + 1;
> > print "$numemp\n";
>
> print "\n", scalar(keys(%count))"\n";
>
>
>
> > }
>
> > sub choosesender
> > {
> > foreach (1..10)
> > {
> > #pick random sender
> > my @sender = ();
> > my $sendernumber = (int rand($numemp));
> > $sender[0] = $senderslist[$sendernumber]; my $newcount =
> > $senderslistcount[$sendernumber]; $newcount = ($newcount+1);
> > splice @senderslistcount,$sendernumber,1,$newcount;
> > }
> > for (my $count = 0; $count <= $#allsenders ; $count++) {
> > print "$count : $senderslist[$count] : $senderslistcount
> [$count]";
> > }
> > }
>
> I'm not sure what this sub is supposed to do, and it is fairly
> unreadable. So I cannot comment on it.
>
>
>
> > getsendersfile();
>
> @allsenders = getsendersfile();
>
> > readsendersfile();
> > choosesender();
>
> I think you want something like this (untested):
>
> #!/usr/bin/perl
>
> use strict;
> use warnings;
>
> sub read_senders {
> my $sendersfile = shift;
> open(my $fh, $sendersfile)
> or die "Cannot open '$sendersfile' for reading. $!";
>
> # Read all lines, split every line on ',', stuff the result
> # in an anonymous array and return an array with references
> # to these anonymous arrays.
> return map [ split /,/ ], <$fh>;
>
> }
>
> sub print_array {
> print $_->[0], ": ", $_->[1], "\n"
> for @_;
>
> }
>
> my @sendercount = read_senders("icc_senders.csv");
>
> # @senderscount now contains an array of arrayreferences
> # look up perldata for more info
>
> print_array(@senderscount);
>
> my $n = int rand(@senderscount);
> $sendercount[$n]->[1]++;
>
> print_array(@senderscount);
>
> HTH,
> M4
Thanks for all the feedback, I shall follow the suggestions and
hopefully see an improvement.
Cheers
Ed
------------------------------
Date: Mon, 10 Mar 2008 19:28:28 GMT
From: "John W. Krahn" <someone@example.com>
Subject: Re: Updating single array element seems to send array out of kilter.
Message-Id: <wZfBj.75260$FO1.71628@edtnps82>
whyatt wrote:
>
> Forgive me for my perl inadequacies, but hopefully it is a very simple
> solution that I am striving for.
>
> The pseudocode of what I am attempting to do is as follows:
> 1. Read contents of a file and parse data into 2 arrays - person and
> count.
> 2. Print out status of current arrays
> 3. Randomly choose one person from array 1 and increment the count by
> 1, updating the associated array element.
> 4. Print out new status of arrays.
>
> The issue I face is that the print in task 2 nicely places each entry
> on a single line, with no use of "\n".
That is because you don't remove the "\n" when you read the file.
> After running task 3, the print in task 4 no longer places each entry
> on a single line, rather causes lines to merge.
When you add 1 to the second (last) field it removes the "\n" at the end
and you don't add one yourself.
> I've scratched my head
> for a day on this now, trying various different things with no luck.
> Perhaps someone in this group can check my code and advise. (The input
> file is a comma separated list)
>
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> +++++++++++++++++++++++
>
> sub getsendersfile
> {
> my $sendersfile = "icc_senders.csv";
> open(FILEHANDLE, $sendersfile) || die "Cannot open file. $!";
> until (eof FILEHANDLE)
Why a loop? In Perl you almost never need to use eof().
> {
> return @allsenders = <FILEHANDLE>;
In list context <FILEHANDLE> returns all records from the file and
subsequent reads from FILEHANDLE will return undef. You are assigning
that list to @allsenders and also returning that list from the
subroutine, but you are calling the subroutine in void context so there
is nowhere for the list to go.
> }
> close FILEHANDLE;
This statement will never be reached because you return before you get here.
> }
>
> sub readsendersfile
> {
> @senderslist = ();
> @senderslistcount = ();
> for (my $count = 0; $count <= $#allsenders ; $count++)
That is usually written as:
for my $count ( 0 .. $#allsenders )
> {
> $senderslist[$count] = ((split ",",$allsenders[$count])[0]);
> $senderslistcount[$count] = ((split ",",$allsenders[$count])[1]);
> print "$count : $senderslist[$count] : $senderslistcount[$count]";
> }
> print "\n";
> $numemp = $#senderslist + 1;
Or simply:
$numemp = @senderslist;
> print "$numemp\n";
> }
>
> sub choosesender
> {
> foreach (1..10)
> {
> #pick random sender
> my @sender = ();
@sender is lexically scoped so it can't be seen outside of this foreach
loop so why are you using it?
> my $sendernumber = (int rand($numemp));
> $sender[0] = $senderslist[$sendernumber];
> my $newcount = $senderslistcount[$sendernumber];
> $newcount = ($newcount+1);
> splice @senderslistcount,$sendernumber,1,$newcount;
That would be more simple and understandable as:
#pick random sender
my $sendernumber = int rand @senderslist;
my @sender = $senderslist[ $sendernumber ];
$senderslistcount[ $sendernumber ]++;
> }
> for (my $count = 0; $count <= $#allsenders ; $count++)
> {
> print "$count : $senderslist[$count] : $senderslistcount[$count]";
> }
> }
>
> getsendersfile();
> readsendersfile();
> choosesender();
>
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> +++++++++++++++++
You probably want something like this:
my $sendersfile = 'icc_senders.csv';
open FILEHANDLE, '<', $sendersfile or die "Cannot open '$sendersfile' $!";
my @data;
while ( <FILEHANDLE> ) {
chomp;
push @data, [ split /,/ ];
print $. - 1, " : $data[-1][0] : $data[-1][1]\n";
}
close FILEHANDLE;
print scalar @data, "\n";
foreach (1..10) {
#pick random sender
my $sendernumber = int rand @data;
my @sender = $data[ $sendernumber ][ 0 ];
$data[ $sendernumber ][ 1 ]++;
}
for my $count ( 0 .. $#data ) {
print "$count : $data[$count][0] : $data[$count][1]\n";
}
John
--
Perl isn't a toolbox, but a small machine shop where you
can special-order certain sorts of tools at low cost and
in short order. -- Larry Wall
------------------------------
Date: Mon, 10 Mar 2008 19:36:44 GMT
From: "John W. Krahn" <someone@example.com>
Subject: Re: Updating single array element seems to send array out of kilter.
Message-Id: <g5gBj.75262$FO1.56947@edtnps82>
Martijn Lievaart wrote:
>
> On Mon, 10 Mar 2008 07:41:03 -0700, whyatt wrote:
>>
>> until (eof FILEHANDLE)
>> {
>> return @allsenders = <FILEHANDLE>;
>> }
>> close FILEHANDLE;
>> }
>
> This is nonsense, return, returns, so the loop is eecuted exactly once.
>
> Replace with:
>
> # use a temporary to force list context
> my @t = <FILEHANDLE>
> return chomp(@t);
From 'perldoc -f chomp':
"It returns the total number of characters removed from all its arguments."
So you are not returning the contents of @t but the number of times that
$/ was removed from @t.
John
--
Perl isn't a toolbox, but a small machine shop where you
can special-order certain sorts of tools at low cost and
in short order. -- Larry Wall
------------------------------
Date: Mon, 10 Mar 2008 16:35:36 +0100
From: Martijn Lievaart <m@rtij.nl.invlalid>
Subject: Re: Updating single array element seems to send array out of kilter.
Message-Id: <pan.2008.03.10.15.35.36@rtij.nl.invlalid>
On Mon, 10 Mar 2008 07:41:03 -0700, whyatt wrote:
> Hi all,
>
> Forgive me for my perl inadequacies, but hopefully it is a very simple
> solution that I am striving for.
>
> The pseudocode of what I am attempting to do is as follows: 1. Read
> contents of a file and parse data into 2 arrays - person and count.
> 2. Print out status of current arrays 3. Randomly choose one person from
> array 1 and increment the count by 1, updating the associated array
> element. 4. Print out new status of arrays.
>
> The issue I face is that the print in task 2 nicely places each entry on
> a single line, with no use of "\n".
Which is strange at first, where does the newline come from? It's tagged
on to the count, because you don't chomp your input.
>
> After running task 3, the print in task 4 no longer places each entry on
> a single line, rather causes lines to merge. I've scratched my head for
> a day on this now, trying various different things with no luck. Perhaps
> someone in this group can check my code and advise. (The input file is a
> comma separated list)
You should have:
- Posted (a small sample of) the inputfile
- Posted a complete program, not hust the snipped you have trouble with.
Without a complete program, it is difficult to check. Some random
comments:
>
> sub getsendersfile
> {
> my $sendersfile = "icc_senders.csv";
> open(FILEHANDLE, $sendersfile) || die "Cannot open file. $!";
Better use lexical filehandles.
open(my $fh, $sendersfile) or die "Cannot open '$sendersfile' for
reading. $!";
> until (eof FILEHANDLE)
> {
> return @allsenders = <FILEHANDLE>;
> }
> close FILEHANDLE;
> }
This is nonsense, return, returns, so the loop is eecuted exactly once.
Replace with:
# use a temporary to force list context
my @t = <FILEHANDLE>
return chomp(@t);
However, you seem to set the global @allsenders as well. So what is the
use of returning something?
>
> sub readsendersfile
This sub does not *read* the file, it parses it. So the name is
misleading.
> {
> @senderslist = ();
> @senderslistcount = ();
Are these globals or locals? This part smells wrong.
> for (my $count = 0; $count <= $#allsenders ; $count++) {
This is a C style loop, Perl has more effective mechanisms.
> $senderslist[$count] = ((split ",",$allsenders[$count])
[0]);
> $senderslistcount[$count] = ((split ",",$allsenders
[$count])[1]);
> print "$count : $senderslist[$count] : $senderslistcount
[$count]";
> }
my %count;
for (@allsenders) {
my ($email, $cnt) = split(/,/);
$count{$email} = $cnt;
print "$email: $cnt\n";
}
You loose the numbering, but do you really need that?
> print "\n";
> $numemp = $#senderslist + 1;
> print "$numemp\n";
print "\n", scalar(keys(%count))"\n";
> }
>
> sub choosesender
> {
> foreach (1..10)
> {
> #pick random sender
> my @sender = ();
> my $sendernumber = (int rand($numemp));
> $sender[0] = $senderslist[$sendernumber]; my $newcount =
> $senderslistcount[$sendernumber]; $newcount = ($newcount+1);
> splice @senderslistcount,$sendernumber,1,$newcount;
> }
> for (my $count = 0; $count <= $#allsenders ; $count++) {
> print "$count : $senderslist[$count] : $senderslistcount
[$count]";
> }
> }
I'm not sure what this sub is supposed to do, and it is fairly
unreadable. So I cannot comment on it.
>
> getsendersfile();
@allsenders = getsendersfile();
> readsendersfile();
> choosesender();
I think you want something like this (untested):
#!/usr/bin/perl
use strict;
use warnings;
sub read_senders {
my $sendersfile = shift;
open(my $fh, $sendersfile)
or die "Cannot open '$sendersfile' for reading. $!";
# Read all lines, split every line on ',', stuff the result
# in an anonymous array and return an array with references
# to these anonymous arrays.
return map [ split /,/ ], <$fh>;
}
sub print_array {
print $_->[0], ": ", $_->[1], "\n"
for @_;
}
my @sendercount = read_senders("icc_senders.csv");
# @senderscount now contains an array of arrayreferences
# look up perldata for more info
print_array(@senderscount);
my $n = int rand(@senderscount);
$sendercount[$n]->[1]++;
print_array(@senderscount);
HTH,
M4
------------------------------
Date: Mon, 10 Mar 2008 09:44:50 -0500
From: Ted Zlatanov <tzz@lifelogs.com>
Subject: Re: Use of "return" in place of "last" (newbie question)?
Message-Id: <86pru2sknx.fsf@lifelogs.com>
On Sun, 09 Mar 2008 17:30:49 +0000 Michael <mike@nospam.co.uk> wrote:
M> Just as a matter of interest, so far as I could see, my technique of
M> setting a flag was the simplest way of maintaining the integrity of the
M> foreach (terminating it with "last" rather than jumping out of it with
M> "return"), whilst not wasting processor cycles performing irrelevant loops
M> later in the function. I am a newbie and don't know much - is there a
M> more elegant alternative which would satisfy the functional programmers?
Don't worry about satisfying functional programmers or anyone else. Get
the task done, write correct maintainable code, and that's enough.
Ted
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
From: Perl-Users-Request@ruby.oce.orst.edu (Perl-Users-Digest Admin)
Subject: Digest Administrivia (Last modified: 6 Apr 01)
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------------------------------
End of Perl-Users Digest V11 Issue 1351
***************************************
