How to find the position of equal elements in character vectors?

Question

How to find the position of equal elements in character vectors?

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#1 by (4 votes)

1

Considering:

a<-c("Ano", "X2751006.", "X2751007.", "X2751008.", "X2751015.", 
     "X2751017.", "X2751018.", "X2751025.", "X2752001.", "X2752006.", 
     "X2752007.", "X2752008.", "X2752009.", "X2752010.", "X2752011.", 
     "X2752012.", "X2752013.", "X2752014.", "X2752017.", "X2752021.", 
     "X2753001.", "X2753002.", "X2753003.", "X2753004.", "X2753005.", 
     "X2753007.", "X2753008.", "X2753009.", "X2753014.")

 b<-c( "X2752013.", "X2752014.","X2753014.")

What is the function that I should apply to know what the position of items b in a , using R?

NOTE: I applied the function which and grep and I was not successful.

r

asked by anonymous 13.11.2015 / 19:25

1 answer

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score 4 · Accepted Answer

If you search for elements in a that are exactly equal to elements in b , the best option is to use %in% :

a<-c("Ano", "X2751006.", "X2751007.", "X2751008.", "X2751015.", 
     "X2751017.", "X2751018.", "X2751025.", "X2752001.", "X2752006.", 
     "X2752007.", "X2752008.", "X2752009.", "X2752010.", "X2752011.", 
     "X2752012.", "X2752013.", "X2752014.", "X2752017.", "X2752021.", 
     "X2753001.", "X2753002.", "X2753003.", "X2753004.", "X2753005.", 
     "X2753007.", "X2753008.", "X2753009.", "X2753014.")

 b<-c( "X2752013.", "X2752014.","X2753014.")

a %in% b
which(a %in% b)

If you want to search for regular expressions, one option is to combine mapply() , grepl() , apply() and unlist() :

apply(unlist(mapply(grepl, a, MoreArgs = list(b))), 1, which)