April 2014
Beginner to intermediate
830 pages
15h 21m
Chinese
Content preview from Mathematica 錦囊妙計
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196
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第五章
延伸資訊
如 果 你 有 一 字 串 串 列， 並 想 擷 取 匹 配 模 式 的 字 串， 此 時 須 使 用
Select
指 令 搭 配
StringMatchQ
作為模式匹配測試，而不是
StringCases
指令，詳見訣竅 4.1。[Page-196]
5.4 字串複製
問題點
你想串接重複的字串為新字串。
解決方案
使用
StringJoin[]
指令串接字串串列。
ch05.indd 196 2014/4/2 上午 06:13:09
5.4 字串複製
|
197
討論說明
這個解法十分簡單，之所以將此問題納入本書，是因為你也許會覺得 Mathematica 應該
要為本功能提供內建指令，但事實上卻付之闕如。對於大多數應用實例，這個解法沒有
問題，但對於大數量的複製動作，另一個複製方法會更有效率。原理是以重複雙倍的動
作複製字串，直到大於指定數目且最接近 2 的冪次方，再擷取指定數目的字串數量。
n * StringLength[seed]
本方法可能有點難解，讓我們仔細看來。純函數
#<>#&
作用於字串串列會將字串複製
（回憶一下，
<>
算符用來串接字串）。[Page-197]
以下則會將字串複製兩次，也就是原字串的 4 倍。
重複進行此步驟
m
次，可以串接原字串的
2^m
倍，然而所需重複次數不見得
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