[R] vectors of matrix as iinput to lapply

Poersching Poersching79 at web.de
Sun Feb 5 20:19:22 CET 2012

Am 05.02.2012 15:54, schrieb Alaios:
> Dear all
> I am using lapply (actually mclapply that share the same syntax).
> I want to call the same function that takes as input a vector. My initial data structure is a matrix that I want to cut it to multiple vectors (one vector for every row of the matrix) and then feed that to the function by using mclapply.
> Could you please help me converting the matrices to nrow times vectors.
> I would like to thank you in advance for your help
> Regards
> Alex
Hi Alex,
I don't know exactly what you mean. A small example would be helpfull. 
But how I understand you, you have different choices:
let x be a matrix
x <- matrix(rnorm(24, 10,5), nrow=6)

you could
1.  cut the matrix in a list of vectors (xi)
xi <- list()
for (i in 1:length(x[,1])) xi[[i]] <- x[i,]
lapply(xi, function(f) f/5)

2. use lapply in a loop
y <- list()
for (i in 1:length(x[,1])) y[[i]] <- lapply(x[i,], function (f) f/5)

3. use lapply in this way
lapply(x[1:length(x[,1]),], function (f) f/5)

4. combine the apply with the lapply function
apply(x,1,function(f) {
   lapply(f, function (g) g/5)

Hope something like this is what you wanted.
Best wishes, Christian

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