# Match function in R

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The** match()** function returns a vector of the position of first occurrence of the vector1 in vector2. If the element of the vector1 does not exist in vector2, NA is returned.

**Syntax: match(vector1, vector2, nomatch = NA_integer_, incomparables = NULL)**

vector1: vector, the values to be matched

vector2: vector, the values to be matched against

nomatch: the value which should be returned when no match is found

incomparables: the vector of values that cannot be matched.

By default the nomatch argument will return NA in case the match is not found in vector2.

According to the R Documentation the **%in%** operator is equivalent to match(). It is a logical vector which indicates whether a match was located for vector1 in vector2. The result value will be either TRUE or FALSE but never NA. So the %in% operator can be useful in if conditions.

**Syntax:** **vector1 %n% vector2**

**Examples:**

print(match(5, c(1,2,9,5,3,6,7,4,5))) [1] 4 5 %in% c(1,2,9,5,3,6,7,4,5) [1] TRUE 8 %in% c(1,2,9,5,3,6,7,4,5) [1] FALSE > v1 <- c("a1","b2","c1","d2") > v2 <- c("g1","x2","d2","e2","f1","a1","c2","b2","a2") > x <- match(v1,v2) > x [1] 6 8 NA 3 > v1 <- c("a1","b2","c1","d2") > v2 <- c("g1","x2","d2","e2","f1","a1","c2","b2","a2") > v1 %in% v2 [1] TRUE TRUE FALSE TRUE > v1 <- c("a1","b2","c1","d2") > v2 <- c("g1","x2","d2","e2","f1","a1","c2","b2","a2") > x <- match(v1,v2, nomatch = 0) > x [1] 6 8 0 3 > v1 <- c("a1","b2","c1","d2") > v2 <- c("g1","x2","d2","e2","f1","a1","c2","b2","a2") > x <- match(v1,v2, nomatch = 0, incomparables = "a1") > x [1] 0 8 0 3

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