Re^3: Replacing values in an array

[muba]

map and grep can be an intimidating functions, but quite useful once you understand them.

Let's consider grep first, since this one is a little simpler to grasp — or at least, that was my experience. grep takes two arguments, the second being a list of elements to work with, the first being the work that you want to have done on that list. You can specify that as a BLOCK, a code reference, or just the name of a function. grep then loops over the list, aliasing $_ to each element in turn, and calls the given piece of code. Then it returns every element for which the code returned a true value.

my @numbers = (0, 0.5, 1, 1.5, 2, 2.5);

# Calling grep with a BLOCK:
my @integers = grep {int($_) == $_} @numbers;
print join(", ", @integers), " are integers.\n";

# Calling grep with a function name:
my @basket = ("apple", undef, undef, undef, "banana", "cherry", undef,
+ "date");
print "The number of elements in \@basket is ", scalar(@basket), "\n";

my @basket_1 = grep defined, @basket;
print "The number of *defined* elements in \@basket is ", scalar(@bask
+et_1), "\n";

See what happens? grep returns the elements of the list you gave it, for which the piece of code returns true. The non-grep equivalents would be:

my @numbers = (0, 0.5, 1, 1.5, 2, 2.5);

# Calling grep with a BLOCK:
my @integers;
for (@numbers) {
    push @integers, $_ if int($_) == $_;
}
print join(", ", @integers), " are integers.\n";

# Calling grep with a function name:
my @basket = ("apple", undef, undef, undef, "banana", "cherry", undef,
+ "date");
print "The number of elements in \@basket is ", scalar(@basket), "\n";

my @basket_1;
for (@basket) {
    push @basket_1, $_ if defined;
}
print "The number of *defined* elements in \@basket is ", scalar(@bask
+et_1), "\n";

Now, map is pretty similar, except that it allows you to change the elements:

my @numbers = 1..10;
my @times_ten = map { $_ * 10 } @numbers;
print join(", ", @times_ten), "\n";

Of course, these are just the basics — the range of things you can do with them is astonishing. I hope this helps you along.