| duplicated {base} | R Documentation |
Determine Duplicate Elements
Description
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.
Usage
duplicated(x, incomparables = FALSE, ...)
## S3 method for class 'array'
duplicated(x, incomparables = FALSE, MARGIN = 1, ...)
Arguments
x |
a vector or a data frame or an array or |
incomparables |
a vector of values that cannot be compared.
Currently, |
... |
arguments for particular methods. |
MARGIN |
the array margin to be held fixed: see
|
Details
This is a generic function with methods for vectors (including lists), data frames and arrays (including matrices).
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 element (in row-major order). This would most
commonly be used to find duplicated rows (the default) or columns
(with MARGIN = 2).
Warning
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).
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth \& Brooks/Cole.
See Also
unique.
Examples
x <- c(9:20, 1:5, 3:7, 0:8)
## extract unique elements
(xu <- x[!duplicated(x)])
## xu == unique(x) but unique(x) is more efficient
duplicated(iris)[140:143]
duplicated(iris3, MARGIN = c(1, 3))