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The frequency of letters in text has often been studied for use in cryptanalysis, and frequency analysis in particular. No exact letter frequency distribution underlies a given language, since all writers write slightly differently. As a rule texts in different languages using the Arabic script (e.g. the Arabic, Old Turkish, Persian and Urdu languages) will have different letter frequencies, most obviously in the case of letters which are not used at all in a language (e.g. the Persian letters پ, چ, گ are not found in written Arabic language texts). Methods encoding the most frequent letters with the shortest symbols were pioneered by telegraph codes, and are used in modern data-compression techniques such as Huffman coding. == What gets counted in input Arabic text? == Chiefly, the Arabic alphabet consists of 28 primary letters, these are letters 1 to 28 in Table 1. However, when scripting in Arabic, the eight modified letters listed in positions 29 to 36 in the same table are used just the same. If these 8 modified forms are lumped back into the primary list based on shape or phonetic similarity, the outcome then is as shown in Table 2. For accurate frequency analysis, each of the 36 letters of Table 1 gets its frequency counted independently. The ordering of the alphabet shown in the tables is more logical than is used by the Unicode standard. Although the full set of Arabic characters includes about ten diacritics as shown in the Figure 1, frequency analysis of Arabic characters is only concerned with computing the frequency of alphabet letters shown in Table 2. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Arabic letter frequency」の詳細全文を読む スポンサード リンク
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