0630 ... PART 3

apply, sapply, lapply 

apply plus :: http://www.r-bloggers.com/using-apply-sapply-lapply-in-r/

m <- matrix(data=cbind(rnorm(30, 0), rnorm(30, 2), rnorm(30, 

5)), nrow=30, ncol=3)

# 행평균

apply(m, 1, mean) 

# 열평균

apply(m, 2, mean)

# 자기자신? == 가로세로 평균?

apply(m, c(1,2), mean)

# UDF 활용

apply(m, 2, function(x) length(x[x<0]))

apply(m, 2, function(x) is.matrix(x))

apply(m, 2, is.vector)

apply(m, 2, length(x[x<0])) # error!!

apply(m, 2, function(x) mean(x[x>0]))

#works on a list or vector of data.

sapply(1:3, function(x) x^2)

# applications

actors <- c("hyn bin","lee na young","won bin","ha jeong woo","shin gu")

sapply(actors, function(x) substr(x, 1, 3))

sapply(actors, function(x)  substr(x, nchar(x)-2, nchar(x)))

# returns list

lapply(1:3, function(x) x^2)

sapply(1:3, function(x) x^2, simplify=F)

unlist(lapply(1:3, function(x) x^2))

apply :: http://www.r-bloggers.com/the-r-apply-function-a-tutorial-with-examples/