Tired of slow split()

splitByRow.R

splitByRow <- function(Y, f){
	require(tidyverse)
	names <- dimnames(Y)
	Y <- as.matrix(Y); dimnames(Y) <- names
	#levels <- sort(unique(f)) %>% as.character
	temp <- split(Y, f=f)
	names <- names(temp)
	ns <- table(f)[names]
	temp <- lapply(1:length(temp), function(i){
		x <- matrix(temp[[i]], ncol=ncol(Y), nrow=ns[[i]], byrow=FALSE)
		colnames(x) <- colnames(Y)
		x
	})
	names(temp) <- names
	temp
}

splitByCol <- function(Y, f){
	require(tidyverse)
	names <- dimnames(Y)
	Y <- as.matrix(Y); dimnames(Y) <- names
	#levels <- sort(unique(f)) %>% as.character
	temp <- split(t(Y), f=f)
	names <- names(temp)
	ns <- table(f)[names]
	temp <- lapply(1:length(temp), function(i){
		x <- matrix(temp[[i]], nrow=nrow(Y), ncol=ns[[i]], byrow=TRUE)
		rownames(x) <- rownames(Y)
		x
	})
	names(temp) <- names
	temp
}