duplicated() determines which elements of a vector or data frame are duplicates of elements with smaller subscripts, and returns a logical vector indicating which elements (rows) are duplicates.
duplicated(x, incomparables = FALSE, ...) ## S3 method for class 'default': duplicated((x, incomparables = FALSE, fromLast = FALSE, nmax = NA, ...)) ## S3 method for class 'array': duplicated((x, incomparables = FALSE, MARGIN = 1, fromLast = FALSE, ...) anyDuplicated(x, incomparables = FALSE, ...)) ## S3 method for class 'default': anyDuplicated((x, incomparables = FALSE, fromLast = FALSE, ...)) ## S3 method for class 'array': anyDuplicated((x, incomparables = FALSE, MARGIN = 1, fromLast = FALSE, ...))
- a vector or a data frame or an array or
- a vector of values that cannot be compared.
FALSEis a special value, meaning that all values can be compared, and may be the only value accepted for methods other than the default. It will be coerced internally to the same type as
- logical indicating if duplication should be considered from the reverse side, i.e., the last (or rightmost) of identical elements would correspond to
duplicated = FALSE.
- the maximum number of unique items expected.
- arguments for particular methods.
- the array margin to be held fixed: see
apply, and note that
MARGIN = 0maybe useful.
These are generic functions with methods for vectors (including lists), data frames and arrays (including matrices).
For the default methods, and whenever there are equivalent method definitions for
anyDuplicated(x, ...) is a “generalized” shortcut for
any(duplicated(x, ...)), in the sense that it returns the index
i of the first duplicated entry
x[i] if there is one, and
anyDuplicated has a relevant method.
The data frame method works by pasting together a character representation of the rows separated by
\r, so may be imperfect if the data frame has characters with embedded carriage returns or columns which do not reliably map to characters.
The array method calculates for each element of the sub-array specified by
MARGIN if the remaining dimensions are identical to those for an earlier (or later, when
fromLast = TRUE) element (in row-major order). This would most commonly be used to find duplicated rows (the default) or columns (with
MARGIN = 2). Note that
MARGIN = 0 returns an array of the same dimensionality attributes as
Missing values are regarded as equal, but
NaN is not equal to
incomparables will never be marked as duplicated. This is intended to be used for a fairly small set of values and will not be efficient for a very large set.
When used on a data frame with more than one column, or an array or matrix when comparing dimensions of length greater than one, this tests for identity of character representations. This will catch people who unwisely rely on exact equality of floating-point numbers!
Character strings will be compared as byte sequences if any input is marked as
Except for factors, logical and raw vectors the default
nmax = NA is equivalent to
nmax = length(x). Since a hash table of size
8*nmax bytes is allocated, setting
nmax suitably can save large amounts of memory. For factors it is automatically set to the smaller of
length(x) and the number of levels plus one (for
Long vectors are supported for the default method of
duplicated, but may only be usable if
nmax is supplied.
duplicated(): For a vector input, a logical vector of the same length as
x. For a data frame, a logical vector with one element for each row. For a matrix or array, and when
MARGIN = 0, a logical array with the same dimensions and dimnames.
anyDuplicated(): a non-negative integer vector of length one.
Using this for lists is potentially slow, especially if the elements are not atomic vectors (see
vector) or differ only in their attributes. In the worst case it is O(n^2).
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
x <- c(9:20, 1:5, 3:7, 0:8) ## extract unique elements (xu <- x[!duplicated(x)]) ## similar, same elements but different order: (xu2 <- x[!duplicated(x, fromLast = TRUE)]) ## xu == unique(x) but unique(x) is more efficient stopifnot(identical(xu, unique(x)), identical(xu2, unique(x, fromLast = TRUE))) duplicated(iris)[140:143] duplicated(iris3, MARGIN = c(1, 3)) anyDuplicated(iris) ## 143 anyDuplicated(x) anyDuplicated(x, fromLast = TRUE)
Documentation reproduced from R 3.0.2. License: GPL-2.