R Programming

Week 3　Loop Functions and Debugging

函式（function)

功能

apply(X, MARGIN, 函式, ...)

vector 或array

MARGIN: 1 -->行，MARGIN : 2 -->列，MARGIN: c(1,2) -->行與列（各要素）

 ( x <- matrix(1:8, ncol=4) )
     [,1] [,2] [,3] [,4]
[1,]    1    3    5    7
[2,]    2    4    6    8
 apply(x, 2, sum)                         # 求各列總値
[1]  3  7 11 15
 apply(x, c(1,2), sqrt)                   # 求各要素平方根
         [,1]     [,2]     [,3]     [,4]
[1,] 1.000000 1.732051 2.236068 2.645751
[2,] 1.414214 2.000000 2.449490 2.828427
各要素加上４:
> apply(x, c(1,2), [x]+4)
Error: unexpected '[' in "apply(x, c(1,2), [" # 找不到所謂的[x]+4　function

> a<-function(x){　# 定義function(x)
x+4                # 為x+4 
}

> a

function(x){x+4}

> x # 再次確認x值

[,1] [,2] [,3] [,4]

[1,] 1 3 5 7

[2,] 2 4 6 8

> apply(x, c(1,2), a)　 # 將a function代入apply求x＋４。　c(1,2)ー＞指定行與列中各要素

[,1] [,2] [,3] [,4]

[1,] 5 7 9 11

[2,] 6 8 10 12

> a<-function(x){x+4} > a function(x){x+4} > x [,1] [,2] [,3] [,4] [1,] 1 3 5 7 [2,] 2 4 6 8 > apply(x, c(1,2), a) [,1] [,2] [,3] [,4] [1,] 5 7 9 11 [2,] 6 8 10 12

參考資料：

http://cse.naro.affrc.go.jp/takezawa/r-tips/r/24.h...

http://web.ntpu.edu.tw/~cflin/Teach/R/R06EN05Expre...