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Determine Duplicate Elements

Source: R/compatibility.r
df_duplicated.Rd

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". However, as of R 4.1, calling this on a data frame with zero columns always returns an empty logical vector. This has repercussions on other functions that use duplicated, such as unique and anyDuplicated. These functions add zero-column data frames as a special case.

Usage

df_duplicated(x, incomparables = FALSE, fromLast = FALSE, ...)

df_unique(x, incomparables = FALSE, fromLast = FALSE, ...)

df_anyDuplicated(x, incomparables = FALSE, fromLast = FALSE, ...)

df_records(x, use_rownames = FALSE, use_colnames = FALSE)

Arguments

x

a data frame.

incomparables

a vector of values that cannot be compared. FALSE is 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 x.

fromLast

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.

...

arguments for particular methods.

use_rownames

a logical, FALSE by default, indicating whether row values should keep the row names from x. Defaults to FALSE.

use_colnames

a logical, FALSE by default, indicating whether row values should keep the column names from x for their elements. Defaults to FALSE.

Value

For df_duplicated, a logical vector with one element for each row.

For df_unique, a data frame is returned with the same columns, but possible fewer rows (and with row names from the first occurrences of the unique rows).

For df_anyDuplicated, an integer or real vector of length one with value the 1-based index of the first duplicate if any, otherwise 0.

For df_records, a list of the row values in x. This is based on a step in duplicated.data.frame. However, for data frames with zero columns, special handling returns a list of empty row values, one for each row in x. Without special handling, this step returns an empty list. This was the cause for duplicated returning incorrect results for zero-column data frames in older versions of R.

See also

df_rbind

Examples

# row values for a 5x0 data frame
x <- data.frame(a = 1:5)[, FALSE, drop = FALSE]
do.call(Map, unname(c(list, x))) # original step returns empty list
#> list()
df_records(x) # corrected version preserves row count
#> [[1]]
#> list()
#> 
#> [[2]]
#> list()
#> 
#> [[3]]
#> list()
#> 
#> [[4]]
#> list()
#> 
#> [[5]]
#> list()
#>