匹配：match与%in%操作符

match{base}

returns a vector of the positions of (first) matches of its first argument in its second.

 

%in%

is a more intuitive interface as a binary operator, which returns a logical vector indicating if there is a match or not for its left operand.

 

match(x,table,nomatch=NA_integer_,incomparables=NUL)

x %in% table

 

区别：

x %in% table：结果为与x等长的TURE/FALSE向量

match(x,table)：结果为与x等长的向量

（1）x[i]在table中未出现，则为NA

（2）x[i]在table中的位序