That needlessly makes operand evaluation order relevant. Change 
  my @keys;
  @new{ @keys } = @orig{ @keys = grep /[adf]/, keys %orig };

[download]
to 
  my @keys = grep /[adf]/, keys %orig;
  @new{ @keys } = @orig{ @keys };

[download]
and you have simpler, clearer code.

In reply to Re^2: grep for hash? by ikegami
in thread grep for hash? by rovf

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