TSDT (version 1.0.8)

reset_factor_levels: reset_factor_levels

Description

Reset the list of levels associated with a factor variable.

Usage

reset_factor_levels(data)

Value

A data.frame with factor variable that now have reset levels.

Arguments

data

A data.frame containing factor variables.

Details

After subsetting a factor variable some factor levels that were previously present may be lost. This is particularly true for relatively rare factor levels. This function resets the list of factor levels to include only the levels currently present.

Examples

ex1 = as.factor( c( rep('A', 3), rep('B',3), rep('C',3) ) )

## The levels associated with the factor variable include the letters A, B, C
ex1  # Levels are A, B, C

## If the last three observations are dropped the value C no longer occurs
## in the data, but the list of associated factor levels still contains C.
## This mismatch between the data and the list of factor levels may cause
## problems, particularly for algorithms that iterate over the factor levels.

ex1 <- ex1[1:6]
ex1 # Levels are still A, B, C, but the data contains only A and B

## If the factor levels are reset the data and list of levels will once again
## be consistent
ex1 <- reset_factor_levels( ex1 )
ex1 # Levels now contain only A and B, which is consistent with data