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Note5_Function_H24071126葉嘉浤.Rmd
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---
title: "Note_Function_H24071126葉嘉浤"
author: "H24071126葉嘉浤"
date: "2020/5/4"
output: html_document
---
# 1.Source
## 1.寫好程式碼
## 2.將程式碼存為XXX.R檔，並用source執行程式碼
## 3.用print或cat才會輸出最後的結果
```{}
*print => 顯示的字元會用引號隔開
*cat => 顯示的字元不用引號，可用"\n"將字元換行
```
```{r,out.width= 450}
knitr::include_graphics("./source.jpg")
#用source執行程式碼
knitr::include_graphics("./source_output.jpg")
```
```{r}
x <- c("A", "B", "C", "D")
print(x)
cat(x)
#用"\n"將字元換行
cat(x[1], "\n",
x[2], "\n", sep = "" )
#找出完美數(使用print)
k <- 1
while(k < 100){
fac <- c()
for(j in 1:k){
if((k %% j) == 0) fac <- c(fac, j)
}
if(k == sum(fac[-length(fac)])){
out <- paste(paste(k, "=", sep=" "),
paste(fac[-length(fac)], collapse = " + "),
sep = " ")
print(out)
}
k <- k+1
}
#找出完美數(使用cat)
k <- 1
while(k < 100){
fac <- c()
for(j in 1:k){
if((k %% j) == 0) fac <- c(fac, j)
}
if(k == sum(fac[-length(fac)])){
cat(paste(k, "=", sep=" "),
paste(fac[-length(fac)], collapse = " + "), "\n")
}
k <- k+1
}
```
# 2.function(一個輸入值)
```{r}
f <- function(x){
3*x + 2
}
f(2); f(3); f(4)
#舉例
make.percent <- function(x){
x.percent <- round(100*x, digits = 1)
x.show <- paste(x.percent, "%", sep = "")
cat(x.show)
}
make.percent(c(0.8933, 0.2344, 0.0764, 0.7736))
ans <- make.percent(c(0.8933, 0.2344, 0.0764, 0.7736))
ans
#輸出為NULL，因為函數值未貼到到ans這個變數
```
## Return
### 將參數透過算式計算後回傳到函式
```{r}
f <- function(x){
return(3*x + 2)
}
f(2)
f <- function(x){
res <- 3*x + 2
}
f(2)
#因為函數算出來的值沒有回傳到函式，所以f(2)未輸出任何結果
#舉例(使用return)
make.percent <- function(x){
x.percent <- round(100*x, digits = 1)
x.show <- paste(x.percent, "%", sep = "")
return(x.show)
}
make.percent(c(0.8933, 0.2344, 0.0764, 0.7736))
ans <- make.percent(c(0.8933, 0.2344, 0.0764, 0.7736))
ans
#舉例(使用invisible)
make.percent <- function(x){
x.percent <- round(100*x, digits = 1)
x.show <- paste(x.percent, "%", sep = "")
invisible(x.show)
}
make.percent(c(0.8933, 0.2344, 0.0764, 0.7736))
#使用invisible不會直接顯示計算結果，需要再命名一個新的變數來輸出結果
ans <- make.percent(c(0.8933, 0.2344, 0.0764, 0.7736))
ans
```
## 函數名稱
### 函數名稱被視為一個物件
### 如果有向量與函數的名稱相同，該名稱的類型為最近使用的類型
```{r}
objA <- function(x){
return(2*x)
}
objA #輸出為一個函數
objA <- objA(4)
objA #輸出為一個向量
```
# 3.function(多個輸入值)
```{r}
f <- function(x, y){
x^2 + y^2
}
f(2, 2); f(2, 3); f(2, 4)
#舉例
make.percent <- function(x, x.digits){
x.percent <- round(100*x, digits = x.digits)
x.show <- paste(x.percent, "%", sep = "")
return(x.show)
}
make.percent(c(0.8933, 0.2344, 0.0764, 0.7736), 0)
make.percent(c(0.8933, 0.2344, 0.0764, 0.7736), 1)
make.percent(c(0.8933, 0.2344, 0.0764, 0.7736), 2)
#參數設定一個預設值
make.percent <- function(x, x.digits = 0){
x.percent <- round(100*x, digits = x.digits)
x.show <- paste(x.percent, "%", sep = "")
return(x.show)
}
make.percent(c(0.8933, 0.2344, 0.0764, 0.7736))
make.percent(c(0.8933, 0.2344, 0.0764, 0.7736), 0)
```
# 4.用function和return輸出多個結果
## list：一種能存放很多不同類型物件的向量
```{r}
X <- list(a = 3, b = c(1,2,3,4,5), c = c("A", "B"))
X
```
### 用 $ 或 [[ ]] 提取list中的元素
$：元素的名稱
[[ ]]：元素的位置或名稱
```{r}
X <- list(a = 3, b = c(1,2,3,4,5), c = c("A", "B"))
X$a
X[[2]]
X[["c"]]
```
建立list
```{r}
create <- list()
length(create)
length(create) <- 2
create[[1]] <- seq(1,5,2)
create
create$plus <- seq(1,5,2)+3 #新命名的物件會放在list的最後面
create
create[[2]]
create[[3]]
names(create)
length(create) #list的長度因為新增一個名為plus的物件所以+1
#舉例
perfect.number <- function(a, b){
k <- a
res <- c()
ans <- list()
while(k < b){
fac <- c()
for(j in 1:k){
if((k %% j) == 0) fac <- c(fac, j)
}
if(k == sum(fac[-length(fac)])) {
res <- c(res, k)
ans[[paste(k)]] <- fac[-length(fac)]
}
k <- k+1
}
ans$number <- res
return(ans)
}
Ans <- perfect.number(1, 100)
Ans
Ans[["28"]]
```