I have a sql wherein I am fetching few records, sorted by full name.
My requirement is to extract chunks of similar names and then do some operation on it.
Say, the sql returns some records containing names like [name1,name1,name2,name3,name3]
I need to split them to [name1,name1] , [name2] , [name3,name3]
I am able to do it, but I am not happy with my implementation as I have to call doSomethingWithNames()twice.
while (my $paRecs = $pStatementHandle->fetchall_arrayref({}, 3)){
foreach my $phRec(#{$paRecs}){
my $pCurrentName = $phRec->{'FULL_NAME'};
if ((scalar(#aParentRecords) eq 0) or ($aParentRecords[-1] eq $pCurrentName)){
push(#aParentRecords, $pCurrentName);
} else {
doSomethingWithNames(\#aParentRecords);
#aParentRecords= ();
push(#aParentRecords, $pCurrentName);
}
}
};
doSomethingWithNames(\#aParentRecords); # This should be inside while loop
I believe am running into this issue because while doesn't go into the loop for
the last iteration as fetch* returns undef.
Sounds basic PERL stuff, but tried many loop constructs with no luck.
Any pointer will be a great help
The trick is to postpone existing the loop by converting it into an infinite loop. This requires checking the loop-terminating condition (!$rows) twice, though.
my $rows = [];
my $prev_name = '';
my #group;
while (1) {
$rows = $sth->fetchall_arrayref({}, 3) if !#$rows;
if (!$rows || $rows->[0]->{FULL_NAME} ne $prev_name)
if (#group) {
do_something(\#group);
#group = ();
}
last if !$rows;
}
$prev_name = $rows->[0]->{FULL_NAME};
push #group, shift(#$rows);
}
Related
I need to compare two Perl object values, one is from a variable and another one is from an array value
ImmediateParent and data contain path directive values(C:\Users\Public\Documents)
while (length(basename(dirname(($immediateParent)))) > 1)
{
$immediateParent = (dirname(($immediateParent)));
my ($dictionaryitem) = $';
my $boolean =0;
foreach $dictionaryitem (#data)
{
if ($immediateParent eq $dictionaryitem->[0])
{
$boolean = 1;
last;
}
}
if ($boolean)
{
last;
}
}
I attempted to compare the values of two paths directories, but the condition always returned true, so it was ineffective. Would you kindly advise me on how to compare two path values?
If Data::Dumper shows
$immediateParent = 'C:\\Users\\Public';
$dictionaryitem = 'C:\\Users\\Public';
then you should compare them directly without array dereference, i.e. remove the ->[0]:
if ($immediateParent eq $dictionaryitem)
The fact that Perl let you dereference a string is weird. Are you not using strict?
Problem : I want to have a list of objects stored so that i can call the corresponding methods at latter point in time
my #tc = ("TC_1","TC_2");
my %obj_list = ();
foreach my $test (#tc) {
$obj_list{$test} = Test->new($test);
}
In the same module file at latter stage where i need to call the corresponding methods of those objects
foreach my $test (keys %obj_list) {
if (some specific condition is satisfied for a test) {
1 --> $obj_list->$test->action();
2 --> $obj_list{$test}->action();
}
}
I tried 1 and 2 and they are not working. Could some one tell me what i could be doing wrong here.Any inputs would be of great help.
Your code is basically correct - other than a few syntax errors.
# Use ( ... ) to initialise an array.
my #tc = ("TC_1","TC_2");
my %obj_list = ();
foreach my $test (#tc) {
$obj_list{$test} = Test->new($test);
}
foreach (keys %obj_list) {
if (some specific condition is satisfied for a test) {
# This version is incorrect
# $obj_list->$key->action();
# This version will work, except you have the
# key in $_, not $key.
$obj_list{$_}->action();
}
}
Adding use strict and use warnings to your code would have helped you find some of these problems.
I am trying to use DBI's selectrow_hashref instead of fetchrow_hashref in order to save a couple lines of code, but it keeps returning the same row of data over and over.
my $select="SELECT * FROM table";
while (my ($user_ref) = $dbh->selectrow_hashref()) {
# $user_ref is the same each time!
}
When I use fetchrow_hashref, everything is fine, and each iteration I get new data.
my $select="SELECT * FROM table";
my $sth = $dbh->prepare($select) || die "prepare: $select: $DBI::errstr";
$sth->execute() || die "execute: $select: $DBI::errstr";
while (my ($user_ref) = $sth->fetchrow_hashref()) {
# works great, new data in $user_ref each iteration
}
Pray tell, what am I doing wrong? Is selectrow_hashref only intended to retrieve a single record? It doesn't seem that way in the doc.
Is selectrow_hashref only intended to retrieve a single record?
Yes.
It doesn't seem that way in the doc.
Well, that documentation says:
It returns the first row of data from the statement.
Which seems pretty clear to me.
Are you looking for selectall_hashref instead?
Update: Actually, I think you want selectall_array:
my $select='SELECT * FROM table';
foreach my $user_ref ($dbh->selectall_array($select, { Slice => {} })) {
# $user_ref is a hash ref
say $user_ref->{some_column};
}
I have a sub in Perl that needs to return a list of array refs to fit in with the rest of the package. The problem is that I don't know in advance how many array refs I will generate. My usual method of pushing the array refs that I generate into an array and returning a reference to that doesn't work with the rest of the code, which I can't change without breaking some legacy stuff.
sub subTrackTable {
my ($self, $experimentName, $subTrackAttr) = #_;
# return nothing if no subtracks required
if ($subTrackAttr eq 'no_sub') {
return;
}
# get distinct values for subtrack attr (eg antibody) from db
my $dbh = $self->dbh();
my $sh = $dbh->prepare("SELECT DISTINCT * blah sql");
$sh->execute();
my #subtrackTable;
while (my ($term, $value) = $sh->fetchrow_array()) {
my $subtrack = [':$value', $value];
push (#subtrackTable, $subtrack);
}
$sh->finish();
# this is hard-coded for one experiment and does what I want
# Want to loop through #subtrackTable and return a list of all the array refs it contains
# Returning nested array refs doesn't work with external code
return ([":H3K4me3", "H3K4me3"],[":H4K20me3", "H4K20me3"]);
}
The problem is that because I am dynamically getting values from a database, I don't know how many there will be. Just returning \#subtrackTable, which would be my usual strategy breaks the rest of the code. If I knew in advance how many there would be I could also do something like
my $a1 = [":$value1", $value1];
my $a2 = [":$value2", $value2];
...
my $an = [":$valuen", $valuen];
return($a1, $a2,...$an);
but I can't see how to make this work with an unknown number of arrayrefs.
Help appreciated!
It looks like you just need to
return #subtrackTable;
Also, this line
my $subtrack = [':$value', $value];
must be changed to use double quotes, like this
my $subtrack = [ ":$value", $value ];
recently started doing perl. I'm reading old code and trying to rewrite some stuff. I've got a question here about hash references.
#declar anon hash ref that will be returned
my $store_hash = {};
foreach my $item (#list)
{
#this will iterate based on list
my $ret_hash = ops_getval($item, $user)
#do some magic here to map $ret_hash into $store_hash
}
ops_getval is a function that returns a type of ref hash. I want to insert those values into $store_hash. How should I approach this? Can I directly do
$store_hash = ops_getval($var1,$var2)
Much appreciated!
I think the standard way to do this is:
#$store_hash{ keys %$ret_hash } = values %$ret_hash;
This merges all of the hashes returned by all of the calls to ops_getval into $store_hash.
An alternate approach that might be clearer to the eye, possibly at the cost of a lot of redundant data copying:
%$store_hash = (%$store_hash, %$ret_hash);
You would do something like:
$store_hash->{$item} = $ret_hash
In general:
$hashref->{$key} = $value
See here for more: http://perldoc.perl.org/perlref.html#Using-References
To be clear, you can use a loop and get this done.
foreach ( keys%{ $ret_hash } ){
$store_hash->{ $_ } = $ret_hash->{ $_ } ;
}