[英]Referencing an element in a 2D array in Perl
I have the following code which reads in a 6x6 array from STDIN and saves it as an array of anonymous arrays. 我有以下代码,该代码从STDIN读取6x6数组并将其保存为匿名数组的数组。 I am trying to print out each element with
$arr[i][j]
, but the code below isn't working. 我正在尝试使用
$arr[i][j]
打印每个元素,但是下面的代码不起作用。 It just prints out the first element over and over. 它只是一遍又一遍地打印出第一个元素。 How am I not accessing the element correctly?
我如何无法正确访问元素?
#!/user/bin/perl
my $arr_i = 0;
my @arr = ();
while ($arr_i < 6){
my $arr_temp = <STDIN>;
my @arr_t = split / /, $arr_temp;
chomp @arr_t;
push @arr,\@arr_t;
$arr_i++;
}
foreach my $i (0..5){
foreach my $j (0..5){
print $arr[i][j] . "\n";
}
}
i
and j
are not the same as the variables you declared in the foreach
lines. i
和j
与您在foreach
行中声明的变量不同。 Change: 更改:
print $arr[i][j] . "\n";
to: 至:
print $arr[$i][$j] . "\n";
warnings
alerted me to this issue. warnings
我意识到了这个问题。 You should add these lines to all your Perl code: 您应该将以下行添加到所有Perl代码中:
use warnings;
use strict;
To demonstrate the Perlish mantra that there's "more than one way to do it": 为了证明Perlish的口头禅,“有多种方法可以做到这一点”:
use 5.10.0; # so can use "say"
use strict;
use warnings qw(all);
sub get_data {
my ($cols, $rows) = @_;
my ($line, @rows);
my $i;
for ($i = 1; $i <= $rows and $line = <DATA>; $i++) {
chomp $line;
my $cells = [ split ' ', $line ];
die "Row $i had ", scalar(@$cells), " instead of $cols" if @$cells != $cols;
push @rows, $cells;
}
die "Not enough rows, got ", $i - 1, "\n" if $i != $rows + 1;
\@rows;
}
sub print_data {
my ($cols, $rows, $data) = @_;
for (my $i = 0; $i < $rows; $i++) {
for (my $j = 0; $j < $cols; $j++) {
say $data->[$i][$j];
}
}
}
my $data = get_data(6, 6);
print_data(6, 6, $data);
__DATA__
1 2 3 4 5 6
a b c d e f
6 5 4 3 2 1
f e d c b a
A B C D E F
7 8 9 10 11 12
Explanation: 说明:
say
, that avoids unsightly print ..., "\\n"
say
,可以避免难看的print ..., "\\n"
get_data
is a function that can be called and/or reused, instead of just being part of the main script get_data
是一个可以调用和/或重用的函数,而不仅是主脚本的一部分 get_data
knows what data-shape it expects and throws an error if it doesn't get it get_data
知道期望的数据形状,如果没有得到它就会抛出错误 [ ... ]
creates an anonymous array and returns a reference to it [ ... ]
创建一个匿名数组并返回对其的引用 get_data
returns an array-reference so data isn't copied get_data
返回数组引用,因此不会复制数据 print_data
is a function too print_data
也是一个功能 for
loop instead of making lists of numbers, which in Perl 5 needs to allocate memory for
循环而不是创建数字列表,这在Perl 5中需要分配内存 There is also a two-line version of the program (with surrounding bits, and test data): 该程序还有两行版本(带有周围的位和测试数据):
use 5.10.0; # so can use "say"
my @lines = map { [ split ' ', <DATA> ] } (1..6);
map { say join ' ', map qq{"$_"}, @$_ } @lines;
__DATA__
1 2 3 4 5 6
a b c d e f
6 5 4 3 2 1
f e d c b a
A B C D E F
7 8 9 10 11 12
Explanation: 说明:
map
is the premier way to iterate over lists of things where you don't need to know how many you've seen (otherwise, a for
loop is needed) map
是遍历不需要知道已经看到多少事物的列表的主要方法(否则,需要for
循环) "
around the cell contents is only to prove they've been processed. Otherwise the second line could just be: map { say join ' ', @$_ } @lines;
"
仅是为了证明它们已被处理。否则,第二行可能只是: map { say join ' ', @$_ } @lines;
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