Extract or replace subsets of factors.

```
# S3 method for factor
[(x, …, drop = FALSE)
# S3 method for factor
[[(x, …)
# S3 method for factor
[(x, …) <- value
# S3 method for factor
[[(x, …) <- value
```

x

a factor

…

a specification of indices -- see `Extract`

.

drop

logical. If true, unused levels are dropped.

value

character: a set of levels. Factor values are coerced to character.

A factor with the same set of levels as `x`

unless `drop = TRUE`

.

When unused levels are dropped the ordering of the remaining levels is preserved.

If `value`

is not in `levels(x)`

, a missing value is
assigned with a warning.

Any `contrasts`

assigned to the factor are preserved
unless `drop = TRUE`

.

The `[[`

method supports argument `exact`

.

# NOT RUN { ## following example(factor) (ff <- factor(substring("statistics", 1:10, 1:10), levels = letters)) ff[, drop = TRUE] factor(letters[7:10])[2:3, drop = TRUE] # }

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