IDL: foreach (制御ブロック)

foreach の要素の順をすぐに忘れてしまうのと、メモランダムに入れていると見つけにくいという理由で、ほんの短い記事ですが独立させました。

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foreach elm, arr [, idx] do begin

endforeach

; elm: 配列 arr の要素, arr: 配列, idx 配列のインデックス

monthlist = [ 'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',$
                    'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec' ]
dayofmonth = [ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ]
foreach monthname, monthlist, im do begin
  ; im is Index for Month
  if( im NE 1 ) then begin
    print, string( monthname + " has", dayofmonth[ im ], " days",$
                       format = '( a, i3, a )' )
  endif else begin
    print, string( monthname + " has", dayofmonth[ im ], " or",$
                       dayofmonth[ im ] + 1, " days",$
                       format = '( a, i3, a, i3, a )' )
  endelse
endforeach; monthname, monthlist, im

; 結果
Jan has 31 days
Feb has 28 or 29 days
Mar has 31 days
Apr has 30 days
May has 31 days
Jun has 30 days
Jul has 31 days
Aug has 31 days
Sep has 30 days
Oct has 31 days
Nov has 30 days
Dec has 31 days