Is there an R function for finding the index of an element in a vector

Question

In R  I have an element x and a vector v  I want to find the first index of an element in v that is equal to x  I know that one way to do this is  which x    v   1    but that seems excessively inefficient  Is there a more direct way to do it   For bonus points  is there a function that works if x is a vector  That is  it should return a vector of indices indicating the position of each element of x in v

User · Answer

the function Position in funprog  base  also does the job  It allows you to pass an arbitrary function  and returns the first or last match   Position f  x  right   FALSE  nomatch   NA integer

User · Answer

The function match works on vectors  x  lt - sample 1 10  x    1   4  5  9  3  8  1  6 10  7  2 match c 4 8  x     1  1 5  match only returns the first encounter of a match  as you requested  It returns the position in the second argument of the values in the first argument  For multiple matching   in  is the way to go  x  lt - sample 1 4 10 replace TRUE  x    1  3 4 3 3 2 3 1 1 2 2 which x  in  c 2 4      1   2  5  9 10   in  returns a logical vector as long as the first argument  with a TRUE if that value can be found in the second argument and a FALSE otherwise

User · Answer

A small note about the efficiency of abovementioned methods    library microbenchmark     microbenchmark      which  Feb     month abb   1        which month abb  in   Feb       Unit  nanoseconds    min     lq    mean median     uq  max neval    891  979 0 1098 00   1031 1135 5 3693   100    1052 1175 5 1339 74   1235 1390 0 7399  100   So  the best one is      which  Feb     month abb   1

[r] Is there an R function for finding the index of an element in a vector?

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