| match {base} | R Documentation |
match 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, incomparables = FALSE) x %in% table
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 the case when no match is
found. Note that it is coerced to integer. |
incomparables |
a vector of values that cannot be matched. Any
value in x matching a value in this vector is assigned the
nomatch value. Currently, FALSE is the only possible
value, meaning that all values can be matched. |
%in% is currently defined as
"%in%" <- function(x, table) match(x, table, nomatch = 0) > 0
Factors, raw vectors and lists are converted to character vectors, and
then x and table are coerced to a common type (the later
of the two types in R's ordering, logical < integer < numeric <
complex < character) before matching.
Matching for lists is potentially very slow and best avoided except in simple cases.
Exactly what matches what is to some extent a matter of definition.
For all types, NA matches NA and no other value.
For real and complex values, NaN values are regarded
as matching any other NaN value, but not matching NA.
A vector of the same length as x.
match: An integer vector giving the position in table of
the first match if there is a match, otherwise nomatch.
If x[i] is found to equal table[j] then the value
returned in the i-th position of the return value is j,
for the smallest possible j. If no match is found, the value
is nomatch.
%in%: A logical vector, indicating if a match was located for
each element of x.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
pmatch and charmatch for (partial)
string matching, match.arg, etc for function argument
matching.
findInterval similarly returns a vector of positions, but
finds numbers within intervals, rather than exact matches.
is.element for an S-compatible equivalent of %in%.
## The intersection of two sets :
intersect <- function(x, y) y[match(x, y, nomatch = 0)]
intersect(1:10,7:20)
1:10 %in% c(1,3,5,9)
sstr <- c("c","ab","B","bba","c","@","bla","a","Ba","%")
sstr[sstr %in% c(letters,LETTERS)]
"%w/o%" <- function(x,y) x[!x %in% y] #-- x without y
(1:10) %w/o% c(3,7,12)