R-Helpers:
There are a matrix x and a factor f. nrow(x) == length(f), e.g.:
x <- matrix(1:6, nrow = 3)
f <- factor(c("daytime", "daytime", "night"))
I want the sum of all elements of rows of "x" for each corresponding level in factor "f",
In this case, I want output like:
"daytime" [1] x[1,1]+x[2,1]+x[1,2]+x[2,2]
"night" [2] x[3,1]+x[3,2]
But, tapply(x,f,sum) or by(x,f,sum) do not work. What other functions can I use?
Thank you very much
Xiao
Apply a function to each cell of a ragged matrix
2 messages · Xiao Liu, Mahmoud K. Okasha
Hi, you could simply use functions such as: time <- dim (3) for ( i in 1:3) time [i] <- x[i,1]+x[i,2] the result of time will be the sum of rows. best regards.. ----- Original Message ----- From: "XIAO LIU" <xiaoliu at jhmi.edu> To: "R Help" <r-help at stat.math.ethz.ch> Sent: Wednesday, February 18, 2004 12:38 AM Subject: [R] Apply a function to each cell of a ragged matrix
R-Helpers:
There are a matrix x and a factor f. nrow(x) == length(f), e.g.:
x <- matrix(1:6, nrow = 3)
f <- factor(c("daytime", "daytime", "night"))
I want the sum of all elements of rows of "x" for each corresponding level
in factor "f",
In this case, I want output like: "daytime" [1] x[1,1]+x[2,1]+x[1,2]+x[2,2] "night" [2] x[3,1]+x[3,2] But, tapply(x,f,sum) or by(x,f,sum) do not work. What other functions can
I use?
Thank you very much Xiao
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