On 14-01-29 6:41 AM, Bill wrote:
Hi. I saw this example and I cannot begin to figure out how it works. Can
anyone give me an idea on this?
n = 9e6
df = data.frame(values = rnorm(n),
ID = rep(LETTERS[1:3], each = n/3),
stringsAsFactors = FALSE)
head(df)
values ID
1 -0.7355823 A
2 -0.4729925 A
3 -0.7417259 A
4 1.7633367 A
5 -0.3006790 A
6 0.6785947 A
The idea is to replace all occurrences of A by 'Text for A'.
He does this:
translator_vector = c(A = 'Text for A',
B = 'Text for B',
C = 'Text for C')
and subset this vector using df$ID:
dum_vectorized = translator_vector[df$ID]
It works but I have no idea why.
He is indexing by name. The translator_vector looks like this:
A B C
"Text for A" "Text for B" "Text for C"
The first element is named A, the second B, the third C.
So translator_vector["A"] is the same as translator_vector[1]. The ID
column in your dataframe is a vector of strings to be used as names, so
each one pulls out one element from the translator_vector.
Duncan Murdoch
Thank you.
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