/ 
Catmandu-1.2022
River stage two • 81 direct dependents • 87 total dependents
/ Catmandu::Iterable

NAME

Catmandu::Iterable - Base role for all iterable Catmandu classes

SYNOPSIS

# Create an example Iterable using the Catmandu::Importer::Mock class
my $it = Catmandu::Importer::Mock->new(size => 10);

my $array_ref = $it->to_array;
my $num       = $it->count;

# Loop functions
$it->each(sub { print shift->{n} });

my $item = $it->first;

$it->rest
   ->each(sub { print shift->{n} });

$it->slice(3,2)
   ->each(sub { print shift->{n} });

$it->take(5)
   ->each(sub { print shift->{n} });

$it->group(5)
   ->each(sub { printf "group of %d items\n" , shift->count});

$it->tap(\&logme)->tap(\&printme)->tap(\&mailme)
   ->each(sub { print shift->{n} });

my $titles = $it->pluck('title')->to_array;

# Select and loop
my $item = $it->detect(sub { shift->{n} > 5 });

$it->select(sub { shift->{n} > 5})
   ->each(sub { print shift->{n} });

$it->reject(sub { shift->{n} > 5})
   ->each(sub { print shift->{n} });

# Boolean
if ($it->any(sub { shift->{n} > 5}) {
 .. at least one n > 5 ..
}

if ($it->many(sub { shift->{n} > 5}) {
 .. at least two n > 5 ..
}

if ($it->all(sub { shift->{n} > 5}) {
 .. all n > 5 ..
}

# Modify and summary
my $it2 = $it->map(sub { shift->{n} * 2 });

my $sum = $it2->reduce(0,sub {
    my ($prev,$this) = @_;
    $prev + $this;
    });

my $it3 = $it->group(2)->invoke('to_array');

# Calculate maximum of 'n' field
my $max = $it->max(sub {
        shift->{n};
});

# Calculate minimum of 'n' field
my $in = $it->min(sub {
        shift->{n};
});

DESCRIPTION

The Catmandu::Iterable class provides many list methods to Iterators such as Importers and Exporters. Most of the methods are lazy if the underlying datastream supports it. Beware of idempotence: many iterators contain state information and calls will give different results on a second invocation.

METHODS

to_array

Return all the items in the iterator as an array ref.

count

Return the count of all the items in the iterator.

add_to

Add all items in the iterator to a Catmandu::Exporter. Returns a true value when the exportwas successful or undef on error.

LOOPING

each(\&callback)

For each item in the iterator execute the callback function with the item as first argument. Returns the number of items in the iterator.

first

Return the first item from the iterator.

rest

Returns an iterator containing everything except the first item.

slice($index,$length)

Returns an new iterator starting at the item at $index returning at most <$length> items.

take($num)

Returns an iterator with the first $num items.

group($num)

Splits the iterator into new iterators each containing $num items.

$it->group(500)->each(sub {
    my $group_it = $_[0];
    $group_it->each(sub {
        my $item = $_[0];
        # ...
    });
});

Note that the group iterators load their items in memory. The last group iterator will contain less than $num item unless the item count is divisible by $num.

interleave(@iterators)

Returns an iterator which returns the first item of each iterator then the second of each and so on.

contains($data)

Alias for includes.

includes($data)

return true if any item in the collection is deeply equal to $data.

tap(\&callback)

Returns a copy of the iterator and executing callback on each item. This method works like the Unix tee command. Use this command to peek into an iterable while it is processing results. E.g. you are writing code to process an iterable and wrote something like:

$it->each(sub {
   # Very complicated routine
   ...
});

Now you would like to benchmark this piece of code (how fast are we processing). This can be done by tapping into the iterator and calling a 'benchmark' subroutine in your program that for instance counts the number of items divided by the execution time.

$it->tap(\&benchmark)->each(sub {
   # Very complicated routine
   ...
});

sub benchmark {
    my $item = shift;
    $start ||= time;
    $count++;

    printf "%d recs/sec\n" , $count/(time - $start + 1) if $count % 100 == 0;
}

Note that the benchmark method already implements this common case.

every($num, \&callback)

Similar to tap, but only calls the callback every $num times. Useful for benchmarking and sampling.

detect(\&callback)

Returns the first item for which callback returns a true value.

detect(qr/..../)

If the iterator contains STRING values, then return the first item which matches the regex.

detect($key => $val)

If the iterator contains HASH values, then return the first item where the value of $key is equal to $val.

detect($key => qr/..../)

If the iterator contains HASH values, then return the first item where the value of $key matches the regex.

detect($key => [$val, ...])

If the iterator contains HASH values, then return the first item where the value of $key is equal to any of the values given.

pluck($key)

Return an iterator that only contains the values of the given $key.

select(\&callback)

Returns an iterator containing only items item for which the callback returns a true value.

select(qr/..../)

If the iterator contains STRING values, then return each item which matches the regex.

select($key => $val)

If the iterator contains HASH values, then return each item where the value of $key is equal to $val.

select($key => qr/..../)

If the iterator contains HASH values, then return each item where the value of $key matches the regex.

select($key => [$val, ...])

If the iterator contains HASH values, then return each item where the value of $key is equal to any of the vals given.

grep( ... )

Alias for select( ... ).

reject(\&callback)

Returns an iterator containing each item for which callback returns a false value.

reject(qr/..../)

If the iterator contains STRING values, then reject every item except those matching the regex.

reject($key => qr/..../)

If the iterator contains HASH values, then reject every item for where the value of $key DOESN'T match the regex.

reject($key => $val)

If the iterator contains HASH values, then return each item where the value of $key is NOT equal to $val.

reject($key => [$val, ...])

If the iterator contains HASH values, then return each item where the value of $key is NOT equal to any of the values given.

sorted

Returns an iterator with items sorted lexically. Note that sorting requires memory because all items are buffered in a Catmandu::ArrayIterator.

sorted(\&callback)

Returns an iterator with items sorted by a callback. The callback is expected to returns an integer less than, equal to, or greater than 0. The following code snippets result in equal arrays:

$iterator->sorted(\&callback)->to_array
[ sort \&callback @{ $iterator->to_array } ]

sorted($key)

Returns an iterator with items lexically sorted by a key. This is equivalent to sorting with the following callback:

$iterator->sorted(sub { $_[0]->{$key} cmp $_[1]->{$key} })

EXTERNAL ITERATOR

Catmandu::Iterable behaves like an internal iterator. next and rewind allow you to use it like an external iterator.

next

Each call to next will return the next item until the iterator is exhausted, then it will keep returning undef.

while (my $data = $it->next) {
  # do stuff
}

$it->next; # returns undef

rewind

Rewind the external iterator to the first item.

$it->next; # => {n => 1}
$it->next; # => {n => 2}
$it->next; # => {n => 3}
$it->rewind
$it->next; # => {n => 1}

Note the the iterator must support this behavior. Many importers are not rewindable.

BOOLEAN FUNCTIONS

any(\&callback)

Returns true if at least one item generates a true value when executing callback.

many(\&callback)

Alias for many.

many(\&callback)

Returns true if at least two items generate a true value when executing callback.

all(\&callback)

Returns true if all the items generate a true value when executing callback.

MAP & REDUCE

map(\&callback)

Returns a new iterator containing for each item the result of the callback. If the callback returns multiple or no items, the resulting iterator will grow or shrink.

fix(...)

Apply a Catmandu::Fix to each item and return the result as new iterator.

reduce([$start],\&callback)

For each item in the iterator execute &callback($prev,$item) where $prev is the optional $start value or the result of the previous call to callback. Returns the final result of the callback function.

invoke($name)

Returns an interator were the method $name is called on every object in the iterable. This is a shortcut for $it-map(sub { $_[0]->$name })>.

max()

Returns the maximum of an iterator containing only numbers.

max(\&callback)

Returns the maximum of the numbers returned by executing callback.

min()

Returns the minimum of an iterator containing only numbers.

min(\&callback)

Returns the minimum of the numbers returned by executing callback.

benchmark()

Prints the number of records processed per second to STDERR.

format(cols => ['key', ...], col_sep => ' | ', header => 1|0)

Print the iterator data formatted as a spreadsheet like table. Note that this method will load the whole dataset in memory to calculate column widths. See also Catmandu::Exporter::Table for a more elaborated method of printing iterators in tabular form.

stop_if(\&callback)

Returns a new iterator thats stops processing if the callback returns false.

# stop after encountering 3 frobnitzes
my $frobnitzes = 0;
$iterator->stop_if(sub {
    my $rec = shift;
    $frobnitzes++ if $rec->{title} =~ /frobnitz/;
    $frobnitzes > 3;
})->each(sub {
    my $rec = shift;
    ...
});

run

Simply invokes the iterator and returns 1 if any records were processed, 0 otherwise.

$it = $it->tap(sub {
    # do something
});
$it = $it->tap(sub {
    # do another thing
});
$it->run

print 'not empty' if $it->run;

SEE ALSO

Catmandu::Iterator.