Multiple matching

Multiple matching between two vectors. Different from R-native match function, where only one match is returned even if there are multiple matches, mmatch returns all of them.

mmatch(x, table, nomatch = NA_integer_)

Arguments

x

vector or NULL: the values to be matched.

table

vector or NULL: the values to be matched against.

nomatch

the value to be returned in case when no match is found.

Value

A list of the same length as the input x vector. Each list item contains the matching indices (similar to match).

Details

Multiple matches can be useful in many cases, and there is no native R function for this purpose. User can write their own functions combining lapplying with match or %in%, our experience however shows that such non-vectorized function can be extremely slow, especially when the x or table vector gets longer.

mmatch delegates the multiple-matching task to a C-level function, which is optimized for speed. Internal benchmarking shows improvement of hundred fold, namely using mmatching costs about 1/100 of the time used by R-implementation.

See also

match

Author

Jitao David Zhang <jitao_david.zhang@roche.com>, C-code was adapted from the program written by Roland Schmucki.

Examples

vec1 <- c("HSV", "BVB", "FCB", "HSV", "BRE", "HSV", NA, "BVB")
vec2 <- c("FCB", "FCN", "FCB", "HSV", "BVB", "HSV", "FCK", NA, "BRE", "BRE")

mmatch(vec1, vec2)
#> $HSV
#> [1] 6 4
#> 
#> $BVB
#> [1] 5
#> 
#> $FCB
#> [1] 1 3
#> 
#> $HSV
#> [1] 6 4
#> 
#> $BRE
#> [1]  9 10
#> 
#> $HSV
#> [1] 6 4
#> 
#> $<NA>
#> [1] 8
#> 
#> $BVB
#> [1] 5
#> 

## compare to match
match(vec1, vec2)
#> [1] 4 5 1 4 9 4 8 5