- 20151001 [R基礎與應用] Ch08 : 建立R函數
- 整理自 R 軟體資料分析基礎與應用 -- Ch08 : 建立R函數
- [ 本次筆記內容 ]
- （一）Hello World
- （二）函數的引數
- [ 前置作業 ] 使用 sprintf()
- 1. 預設引數值
- 2. 附加引數
- （三）值的回傳
- （四）do.call
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整理自 R 軟體資料分析基礎與應用 -- Ch08 : 建立R函數
（一）Hello World
> # "say.hello"是函數名稱(裡面的"."是普通字元，沒有特殊意義)> # 函數"function()以"{...}"裡面的內容作為函數主體> say.hello <- function()+ {+ print("Hello, World!")+ }>>> say.hello # 呼叫函數function(){ print("Hello, World!")}（二）函數的引數
> # 取代一個特殊輸入字元> sprintf("Hello %s", "Danny")[1] "Hello Danny">>> # 取代兩個特殊輸入字元> sprintf("Hello %s, today is %s", "Danny", "Friday")[1] "Hello Danny, today is Friday"> # 用sprintf建立字串,並以輸入的引數來決定顯示結果> hello.person <- function(name)+ {+ print(sprintf("Hello %s", name))+ }>> hello.person("Danny")[1] "Hello Danny">> hello.person("John")[1] "Hello John">> hello.person("Manami")[1] "Hello Manami">> hello.person("Mason")[1] "Hello Mason">> hello.person("Martial Art")[1] "Hello Martial Art">> hello.person("Parkour")[1] "Hello Parkour"> hello.person <- function(first, last)+ {+ print(sprintf("Hello %s %s", first, last))+ }>> # 透過引數相對位置> hello.person("Danny", "Mason")[1] "Hello Danny Mason">>> # 透過引數名稱> hello.person(first = "Danny", last = "Mason")[1] "Hello Danny Mason">>> # 把引數反過來> hello.person(last = "Mason", first = "Danny")[1] "Hello Danny Mason">>> # 只指定到一個引數名稱> hello.person("Danny", last = "Mason")[1] "Hello Danny Mason">>> # 指定另一個引數名稱> hello.person(first = "Danny", "Mason")[1] "Hello Danny Mason">>> # 透過引數名稱指定第二個引數, 接著在沒輸入引數名稱下指定第一個引數> hello.person(last = "Mason", "Danny")[1] "Hello Danny Mason">> hello.person <- function(first, last = "Doe") # 以"Doe"作為預設的姓氏(last name)+ {+ print(sprintf("Hello %s %s", first, last))+ }>>> # 呼叫函數時不指定姓氏> hello.person("Jared")[1] "Hello Jared Doe">>> # 呼叫函數時指定其它的姓氏> hello.person("Jared", "Lander")[1] "Hello Jared Lander">> # 呼叫 hello.person, 並加入額外的引數> hello.person("Jared", extra = "Goodbye")Error in hello.person("Jared", extra = "Goodbye") : unused argument (extra = "Goodbye")>>> # 以兩個有效引數呼叫函數, 第三個引數是額外的> hello.person("Jared", "Lander", "Goodbye")Error in hello.person("Jared", "Lander", "Goodbye") : unused argument ("Goodbye")>>> # 現在建立 hello.person, 並加入 "..." 引數以接受附加引數> hello.person <- function(first, last = "Doe", ... )+ {+ print(sprintf("Hello %s %s", first, last))+ }>>> # 呼叫 hello.person, 並加入額外的引數> hello.person("Jared", extra = "Goodbye")[1] "Hello Jared Doe">>> # 以兩個有效引數呼叫函數, 第三個引數是額外的> hello.person("Jared", "Lander", "Goodbye")[1] "Hello Jared Lander">（三）值的回傳
>> # 建立函數時不使用 return 指令> double.num <- function(x)+ {+ x * 2+ }>> double.num(5)[1] 10>>> # 使用 return 指令建立> double.num <- function(x)+ {+ return(x * 2)+ }>> double.num(5)[1] 10>>> # 再次建立函數, 這次在 return 後面也放一些指令> double.num <- function(x)+ {+ return(x * 2) # 函數在這裡退出+++ #---以下指令不會被執行, 因為函數已經被退出了---+ print("Hello !")+ return(17)+ #----------------------------------------------+ }>> double.num(5)[1] 10>（四）do.call
>> do.call("hello.person", args = list(first = "Jared", last = "Lander"))[1] "Hello Jared Lander">> do.call(hello.person, args = list(first = "Jared", last = "Lander"))[1] "Hello Jared Lander">>> run.this <- function(x, func = mean)+ {+ do.call(func, args = list(x))+ }>>> # 用預設的 mean 函數找平均值> run.this(1:10)[1] 5.5>>> # 指定要找平均值> run.this(1:10, mean)[1] 5.5>>> # 計算總和> run.this(1:10, sum)[1] 55>>> # 計算標準差> run.this(1:10, sd)[1] 3.02765>