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 sort {} grep {} @foo;

#!/usr/local/bin/perl -w

...
        @$array[$i,$j] = @$array[$j,$i];
    }
}

Benchmark: timing 20 iterations of grep_sort, sort_grep...
 grep_sort:  5 wallclock secs ( 4.70 usr +  0.02 sys =  4.72 CPU) @  4
+.24/s (n=20)
 sort_grep: 16 wallclock secs (15.56 usr +  0.03 sys = 15.59 CPU) @  1
+.28/s (n=20)