As well as allowing direct access to individual array elements, Perl also provides various other interesting ways to deal with arrays. In particular, there are functions that make it very easy and efficient to use a Perl array as a stack or as a queue.
pop
The pop function will remove and return the last element of an array.
In this first example you can see how, given an array of 3 elements, the pop function
removes the last element (the one with the highest index) and returns it.
my @names = ('Foo', 'Bar', 'Baz');
my $last_one = pop @names;
print "$last_one\n"; # Baz
print "@names\n"; # Foo Bar
In the special case of the original array being empty, the pop function
will return undef.
push
The push function can add one or more values to the end of an array.
(Well, it can also add 0 values, but that's not very useful, is it?)
my @names = ('Foo', 'Bar');
push @names, 'Moo';
print "@names\n"; # Foo Bar Moo
my @others = ('Darth', 'Vader');
push @names, @others;
print "@names\n"; # Foo Bar Moo Darth Vader
In this example we originally had an array with two elements. Then we pushed a single scalar value to the end and our array got extended to a 3-element array.
In the second call to push, we pushed the content of the @others
array to the end of the @names array, extending it to a 5-element array.
shift
If you imagine the array starting on the left hand side,
the shift function will move the whole array one unit to the left.
The first element will "fall off" the array and become the function's return value.
(If the array was empty, shift will return undef.)
After the operation, the array will be one element shorter.
my @names = ('Foo', 'Bar', 'Moo');
my $first = shift @names;
print "$first\n"; # Foo
print "@names\n"; # Bar Moo
This is quite similar to pop, but it works on the lower end of the array.
unshift
This is the opposite operation of shift. unshift will
take one or more values (or even 0 if that's what you like) and place it at the
beginning of the array, moving all the other elements to the right.
You can pass it a single scalar value, which will become the
first element of the array. Or, as in the second example, you can pass a second
array and then the elements of this second array (@others in our case)
will be copied to the beginning of the main array (@names in our case)
moving the other elements to higher indexes.
my @names = ('Foo', 'Bar');
unshift @names, 'Moo';
print "@names\n"; # Moo Foo Bar
my @others = ('Darth', 'Vader');
unshift @names, @others;
print "@names\n"; # Darth Vader Moo Foo Bar
Comments
how to replace only the 5th element of an array from an variable.. i am looking up on a value and need to update the 5th element... basically i need to translate the value in an array..
have you tried to read this https://perlmaven.com/perl-arrays
It would be probably easier to help if you showed what was in @values and what are you expecting in @results as I don't know what do you mean by "translate"
@values contains comma delimited strings... 170, test, best, try, 0.1314 @others='CIF'... so i need to translate 4th element of @values(try) to @others('CIF');
so @results =170, test, best, CIF, 0.1314
Don't explain with words. Show the actual data. Show a piece of code e.g. @values = ('170, test, best, try, 0.1314'); Is that it? How does @results look like, the one you wrote is not syntactically correct perl.
test1.csv 170, test, best, try, 0.1314 171, test, best, try, 0.1695 172, test, best, try, 0.1784
while <file =="" test1.csv="">{ @values = split ',', file ;
@others = 'CIF';
@results = splice @values, 5, 0, @others; } O/P: 170, test, best, CIF, 0.1314 171, test, best, CIF, 0.1695 172, test, best, CIF, 0.1784
i hope this is clear.. basically i am looking up for a value..and replacing with the 4th element of an array if the value matches.. just mentioned the high level code..
That does not look like working Perl code. Is this what you run? Do you actually need anything in your perl script or is this your real task: "given a CSV file replace the 4th column with the string 'CIF'" ?
yes.. given a CSV file.. replace the 4th column with string 'CIF'.. i have just given a high level code.. string 'CIF' is being looked upon from a table..
What table? Based on what do you look it up?
that part of code is working fine.. i am looking up value from 4th column of the file.. and replacing it with the output i get from the table..
@results = splice @values, 5, 0, @others; what is wrong with this line.. ?
You wrote CIF is looked upon from a table but in your example @others is a one-element array. Not a table and there is no "looking up" it seems to be always CIF. So what did you mean by "looked upon from a table"?
yes.. i am loading a variable from the table lookup (which i have not mentioned in the code here).. and then passing it to @others which is one element array... so just mentioned string 'CIF' here.. now how can i replace the 4th column of the CSV to the value from @others...?
$values[3] = 'CIF'; $values[3] = others[0];
Thanks for the explanation, it really helped me a lot.
Nice explanation. Thanks man
