SAS Fuctions

1. monotonic(), 单调递增函数。返回一列变量的序列等，类似于_N_ 。

2. index v indexw:

INDEX Function Searches a character expression for a string of characters, and returns the position of the string’s first character for the first occurrence of the string.

INDEXW Function Searches a character expression for a string that is specified as a word, and returns the position of the first character in the word.

INDEXC Function Searches a character expression for any of the specified characters, and returns the position of that character.

eg.   if effect = 'ps_imp_des_xx' , then

　　index(effect, 'ps_imp') = 1, index(effect,  'ps_imp_des' ) =1.

　　indexw( effect, 'ps_imp') =1, indexw(effect,  'ps_imp_des' ) =0.