Vectorize for-loop

Question

I have the following data:

Letters <- c("A","B","C")
Numbers <- c(1,0,1)
Numbers <- as.integer(Numbers)

Data.Frame <- data.frame(Letters,Numbers)

I want to create a Dummy Variable for the Letters and wrote the following for-loop:

for(level in unique(Data.Frame$Letters)){Data.Frame[paste("", level, sep = "")]
<- ifelse(Data.Frame$Letters == level, 1, 0)}

Is there a way to vectorize this for-loop? Is the following use of dcast alredy vectorized?

dt <- data.table(Letters,Numbers)
dcast.data.table(dt, Letters+Numbers~Letters,fun.aggregate=length)

Rich Scriven · Accepted Answer · 2018-12-16 17:29:54Z

1

You could use outer

cbind(Data.Frame, +outer(Letters, setNames(nm=Letters), "=="))
#   Letters Numbers A B C
# 1       A       1 1 0 0
# 2       B       0 0 1 0
# 3       C       1 0 0 1

answered Dec 16, 2018 at 17:29

Rich Scriven

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2 Comments

Mucteam Over a year ago

Thank you very much. And this is vectorized because the outer function is applying "==" to the two vectors Letters and setNames(nm=Letters)?

Rich Scriven Over a year ago

outer is a vectorized function, yes. (i.e. there are no internal loops)

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