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I was trying to change few levels in my factor variable by simply coercing characters on that factor variable but it dint seem to work.

`data(iris)`

iris$Species <- rep("Random", 71)

`## Warning: invalid factor level, NAs generated`

`iris$Species`

`## [1] setosa setosa setosa setosa setosa setosa setosa `

## [8] setosa setosa setosa setosa setosa setosa setosa

## [15] setosa setosa setosa setosa setosa setosa setosa

## [22] setosa setosa setosa setosa setosa setosa setosa

## [29] setosa setosa setosa setosa setosa setosa setosa

## [36] setosa setosa setosa setosa setosa setosa setosa

## [43] setosa setosa setosa setosa setosa setosa setosa

## [50]

## [57]

## [64]

## [71]

## [78]

## [85]

## [92]

## [99]

## [106]

## [113]

## [120] virginica virginica virginica virginica virginica virginica

## [127] virginica virginica virginica virginica virginica virginica virginica

## [134] virginica virginica virginica virginica virginica virginica virginica

## [141] virginica virginica virginica virginica virginica virginica virginica

## [148] virginica virginica virginica

## Levels: setosa versicolor virginica

Well, I did find a way to find a work around for that by doing this:

`iris$Species <- as.character(iris$Species)`

iris$Species <- rep("Random", 71)

iris$Species <- as.factor(iris$Species)

iris$Species

`## [1] setosa setosa setosa setosa setosa setosa setosa `

## [8] setosa setosa setosa setosa setosa setosa setosa

## [15] setosa setosa setosa setosa setosa setosa setosa

## [22] setosa setosa setosa setosa setosa setosa setosa

## [29] setosa setosa setosa setosa setosa setosa setosa

## [36] setosa setosa setosa setosa setosa setosa setosa

## [43] setosa setosa setosa setosa setosa setosa setosa

## [50] Random Random Random Random Random Random Random

## [57] Random Random Random Random Random Random Random

## [64] Random Random Random Random Random Random Random

## [71] Random Random Random Random Random Random Random

## [78] Random Random Random Random Random Random Random

## [85] Random Random Random Random Random Random Random

## [92] Random Random Random Random Random Random Random

## [99] Random Random Random Random Random Random Random

## [106] Random Random Random Random Random Random Random

## [113] Random Random Random Random Random Random Random

## [120] Random virginica virginica virginica virginica virginica virginica

## [127] virginica virginica virginica virginica virginica virginica virginica

## [134] virginica virginica virginica virginica virginica virginica virginica

## [141] virginica virginica virginica virginica virginica virginica virginica

## [148] virginica virginica virginica

## Levels: Random setosa virginica

This problem annoyed me at first, “Why would R not allow me to change/add factor [email protected]#[email protected]#?” but then Utkarsh and I had a conversation about this which made me think otherwise.

Excerpts from the conversation:

Utkarsh: It is usually not good to create data on the fly. Besides, when you create a factor variable, you should give the finite set of values it can take. This prevents future mistakes. It is called type checking. Python does not do it. R does it to some extent. C does it to some extent. Haskell does it very very strictly and it prevents about 50% of bugs from appearing. Let's say you misspell one of the levels.

In retrospect, it actually makes sense for us not to be able to add/edit the levels in factor variables. For a simple reason, we “might” make mistake, and misspelling a factor level could cause serious trouble. Lesson learnt!

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