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rstatisticslevels

Values are changing while matching levels in R.

I have 2 variables x and y. In X I have only 1 value with 1 level. I want to match levels of y to x. After matching levels, level's are matching but value of X is changing. Why this is so ?

x = as.factor(c(3))    
> x
3
Levels: 3

y = as.factor(c(2,3,4))
> y
2 3 4
Levels: 2 3 4

Output -

levels(x) = levels(y)

print(x)
 2

Levels: 2 3 4

The initial value of X was 3 now its 2.

Solution

  • I think this occurs because R presents the new level and not the value. For example, if you will do as.numeric(x) it will present 1 and not 3. 

    x <- as.factor(c(3))  
as.numeric(x)

    [1] 1

    However, if you will unfactor the variable using varhandle::unfactor(), it will present the "real" value. 

    varhandle::unfactor(x)

    [1] 3

    Thus, when you do levels(x) <- levels(y) you don't relevel/refactor the levels of x to be like y - you adjusting/changing the levels and values. 

    x <- as.factor(c(3))  
y <- as.factor(c(2,3,4))
levels(x) <- levels(y)
unfactor(x)

    [1] 2

    Doing thisx <- factor(x, levels = union(levels(x), levels(y))) will solve your problem. 

    x <- as.factor(c(3))  
y <- as.factor(c(2,3,4))
x

    [1] 3 Levels: 3

    x <- factor(x, levels = union(levels(x), levels(y)))
x

    [1] 3 Levels: 2 3 4

    unfactor(x)

    [1] 3

    Thank you @pieca for the comment.