The following two statements are equivalent (EXPR represents a logical expression).

@selected = grep EXPR, @input;
@selected = map { if (EXPR) { $_ } } @input;
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That's not really true. Your second one, for each element, will be either $_ (if EXPR is true) or EXPR if it's false. The usual way to make map like grep is with the ternary operator as below.

use Data::Dumper;

my @x = qw( foo bar );
print       q[ map { if (0) { $_ } } @x ], "\n";
print Dumper [ map { if (0) { $_ } } @x ];

print "\n", q[ grep 0, @x ], "\n";
print Dumper [ grep 0, @x ];

print "\n", q[ map { 0 ? $_ : () } @x ], "\n";
print Dumper [ map { 0 ? $_ : () } @x ];
__END__
 map { if (0) { $_ } } @x
$VAR1 = [ 
          0,
          0
        ];

 grep 0, @x
$VAR1 = [];

 map { 0 ? $_ : () } @x
$VAR1 = [];
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