On Apr 30, 2011, at 4:18 PM, Alice Wines wrote:
Hello all,
I have a quandry I have been scratching my head about for a
while. I've searched the manual and the web and have not been able to
find an acceptable result, so I am hoping for some help.
I have two data frames and I want to index into the first using
the second, and replace the specific values I have indexed with more
values from the second data.frame. I can do this using a loop, but I
wanted a quicker solution with no loops involved.
Although my data set is much larger than this, a small example of what
I am trying to do is as follows:
df1 <- data.frame(rows=c("A","B","C", "B", "C", "A"),
columns=c("21_2", "22_2", "23_2", "21_2", "22_2", "23_2"),
values=c(3.3, 2.5, 67.2, 44.3, 53, 66))
df2 <- data.frame(matrix(rep(NA, length(df1$values)),nrow=3, ncol=3))
names(df2) <- c("21_2", "22_2", "23_2")
row.names(df2) <- c("A", "B", "C")
df1
rows columns values
1 A 21_2 3.3
2 B 22_2 2.5
3 C 23_2 67.2
4 B 21_2 44.3
5 C 22_2 53.0
6 A 23_2 66.0
> require(Matrix)
> xtabs(values~rows+columns, data=df1, sparse=TRUE)
3 x 3 sparse Matrix of class "dgCMatrix"
21_2 22_2 23_2
A 3.3 . 66.0
B 44.3 2.5 .
C . 53.0 67.2
df2
21_2 22_2 23_2
A NA NA NA
B NA NA NA
C NA NA NA
Note that none of the same locations in df2 are specified twice
in df2, so I'm not worried about over-writing it.
I have tried 'mapply' and 'replace', but apparently either they do
not work well for this or I don't understand how to use them properly
for this purpose. My understanding is that 'replace' needs a vector
input and that one cannot create a vector of vectors, so I couldn't
pass my indices to 'replace'.
When I tried mapply, the code I used was something like what
follows:
df3 <- mapply('[<-' , df2, paste(as.character(df1$rows),
as.character(df1$columns), sep=', '), df1$values)
but it yields the following strange result
df3
21_2 22_2 23_2 <NA> <NA> <NA>
NA NA NA NA NA NA
NA NA NA NA NA NA
NA NA NA NA NA NA
A, 21_2 3.3 2.5 67.2 44.3 53 66
What I want to see is the following:
df3
21_2 22_2 23_2
A 3.3 NA 66.0
B 44.3 2.5 NA
C NA 53.0 67.2
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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