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What if one wants to apply a functon i.e. to each row of a matrix, but also wants to use as an argument for this function the number of that row. As an example, suppose you wanted to get the n-th root of the numbers in each row of a matrix, where n is the row number. Is there another way (using apply only) than column-binding the row numbers to the initial matrix, like this?
test <- data.frame(x=c(26,21,20),y=c(34,29,28)) t(apply(cbind(as.numeric(rownames(test)),test),1,function(x) x[2:3]^(1/x[1]))) P.S. Actually if test was really a matrix : test <- matrix(c(26,21,20,34,29,28),nrow=3) , rownames(test) doesn't help :( Thank you.
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You can use the apply() function to apply a function to each row in a matrix or data frame in R. where: X: Name of the matrix or data frame. MARGIN: Dimension to perform operation across.
The lapply() function helps us in applying functions on list objects and returns a list object of the same length. The lapply() function in the R Language takes a list, vector, or data frame as input and gives output in the form of a list object.
mapply is a multivariate version of sapply . mapply applies FUN to the first elements of each ... argument, the second elements, the third elements, and so on. Arguments are recycled if necessary.
What I usually do is to run sapply on the row numbers 1:nrow(test) instead of test, and use test[i,] inside the function:
t(sapply(1:nrow(test), function(i) test[i,]^(1/i))) I am not sure this is really efficient, though.
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