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4.2. Printing a List with Commas
4.2.1. Problem
You'd like to print out a list
containing an unknown number of elements, placing an "and" before the
last element and commas between each element if there are more than
two.
4.2.2. Solution
Use this function, which returns the formatted string:
sub commify_series {
(@_ = = 0) ? :
(@_ = = 1) ? $_[0] :
(@_ = = 2) ? join(" and ", @_) :
join(", ", @_[0 .. ($#_-1)], "and $_[-1]");
}4.2.3. Discussion
It often looks odd to print out arrays:
@array = ("red", "yellow", "green");
print "I have ", @array, " marbles.\n";
print "I have @array marbles.\n";
I have redyellowgreen marbles.
I have red yellow green marbles.What you really want it to say is, "I
have red,
yellow, and
green marbles". The function
given in the solution generates strings in that format. The word
"and" is placed between the last two list
elements. If there are more than two elements in the list, a comma is
placed between every element.Example 4-1 gives a complete demonstration of the
function, with one addition: if any element in the list already
contains a comma, a semicolon is used for the separator character
instead.
Example 4-1. commify_series
#!/usr/bin/perl -w
# commify_series - show proper comma insertion in list output
# @lists is an array of (references to anonymous) arrays
@lists = (
[ 'just one thing' ],
[ qw(Mutt Jeff) ],
[ qw(Peter Paul Mary) ],
[ 'To our parents', 'Mother Theresa', 'God' ],
[ 'pastrami', 'ham and cheese', 'peanut butter and jelly', 'tuna' ],
[ 'recycle tired, old phrases', 'ponder big, happy thoughts' ],
[ 'recycle tired, old phrases',
'ponder big, happy thoughts',
'sleep and dream peacefully' ],
);
foreach $aref (@lists) {
print "The list is: " . commify_series(@$aref) . ".\n";
}
# demo for single list
@list = qw(one two three);
print "The last list is: " . commify_series(@list) . ".\n";
sub commify_series {
my $sepchar = grep(/,/ => @_) ? ";" : ",";
(@_ = = 0) ? ' :
(@_ = = 1) ? $_[0] :
(@_ = = 2) ? join(" and ", @_) :
join("$sepchar ", @_[0 .. ($#_-1)], "and $_[-1]");
}
Here's the output from the program:
The list is: just one thing.
The list is: Mutt and Jeff.
The list is: Peter, Paul, and Mary.
The list is: To our parents, Mother Theresa, and God.
The list is: pastrami, ham and cheese, peanut butter and jelly, and tuna.
The list is: recycle tired, old phrases and ponder big, happy thoughts.
The list is: recycle tired, old phrases; ponder
big, happy thoughts; and sleep and dream peacefully.
The last list is: one, two, and three.
As you see, we don't follow the ill-advised practice of omitting the
final comma from a series under any circumstances. To do so
introduces unfortunate ambiguities and unjustifiable exceptions. The
examples shown would have claimed that we were the offspring of
Mother Teresa and God, and would have had us eating sandwiches made
of jelly and tuna fish mixed together atop the peanut butter.
4.2.4. See Also
Fowler's Modern English Usage; we explain the
nested list syntax in Recipe 11.1; the
grep function in perlfunc(1)
and Chapter 29 of Programming Perl; the
conditional operator ("?:") is discussed in
perlop(1) and in the "Conditional Operator"
section of Chapter 3 of Programming Perl
