duplicated {base}R Documentation

Determine Duplicate Elements


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 'array':
duplicated(x, incomparables = FALSE, MARGIN = 1, ...)


x a vector or a data frame or an array or NULL.
incomparables a vector of values that cannot be compared. Currently, FALSE is the only possible value, meaning that all values can be compared.
... arguments for particular methods.
MARGIN the array margin to be held fixed: see apply.


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).


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.

See Also



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(iris3, MARGIN = c(1, 3))

[Package base version 2.5.0 Index]