R语言笔记(四):函数

文章目录

  • [一、Function basics](#一、Function basics)
    • [1、Creating your own function](#1、Creating your own function)
    • [2、Function structure](#2、Function structure)
    • [3、Using your created function](#3、Using your created function)
    • [4、Multiple inputs](#4、Multiple inputs)
    • [5、Default inputs](#5、Default inputs)
  • [二、Return values and side effects](#二、Return values and side effects)
    • [1、Returning more than one thing](#1、Returning more than one thing)
    • [2、Side effects](#2、Side effects)
      • [Example of side effect: plot](#Example of side effect: plot)
  • [三、Environments and design](#三、Environments and design)
    • [1、Environment: what the function can see and do](#1、Environment: what the function can see and do)
    • [2、Environment examples](#2、Environment examples)

一、Function basics

1、Creating your own function

Call function() to create your own function. Document your function with comments

c 复制代码
# get.wordtab.king: get a word table from King's "I Have A Dream" speech
# Input: none
# Output: word table, i.e., vector with counts as entries and associated
#         words as names

get.wordtab.king = function() {
  lines = readLines("https://raw.githubusercontent.com/king.txt")
  text = paste(lines, collapse=" ")
  words = strsplit(text, split="[[:space:]]|[[:punct:]]")[[1]]
  words = words[words != ""]
  wordtab = table(words)
  return(wordtab)
}
  • Input: none
  • Output: word table, i.e., vector with counts as entries and associated words as names

Much better: create a word table function that takes a URL of web

c 复制代码
# get.wordtab.from.url: get a word table from text on the web
# Input:
# - str.url: string, specifying URL of a web page 
# Output: word table, i.e., vector with counts as entries and associated
#   words as names

get.wordtab.from.url = function(str.url) {
  lines = readLines(str.url)
  text = paste(lines, collapse=" ")
  words = strsplit(text, split="[[:space:]]|[[:punct:]]")[[1]]
  words = words[words != ""]
  wordtab = table(words)
  return(wordtab)
}
  • Input:

    • str.url: string, specifying URL of a web page
  • Output: word table, i.e., vector with counts as entries and associated words as names

2、Function structure

The structure of a function has three basic parts:

  • Inputs (or arguments ): within the parentheses of function()
  • Body (code that is executed): within the braces {}
  • Output (or return value ): obtained with function return()
  • (optional) Comments: description of functions by comments
c 复制代码
# get.wordtab.from.url: get a word table from text on the web
# Input:
# - str.url: string, specifying URL of a web page 
# Output: word table, i.e., vector with counts as entries and associated
#   words as names

get.wordtab.from.url = function(str.url) {
  lines = readLines(str.url)
  text = paste(lines, collapse=" ")
  words = strsplit(text, split="[[:space:]]|[[:punct:]]")[[1]]
  words = words[words != ""]
  wordtab = table(words)
  return(wordtab)
}

3、Using your created function

Our created functions can be used just like the built-in ones

c 复制代码
# Using our function
king.wordtab.new = get.wordtab.from.url(
  "https://raw.githubusercontent.com/mxcai/BIOS5801/main/data/king.txt")
all(king.wordtab.new == king.wordtab)
## [1] TRUE

# Revealing our function's definition
get.wordtab.from.url
## function(str.url) {
## lines = readLines(str.url)
## text = paste(lines, collapse=" ")
## words = strsplit(text, split="[[:space:]]|[[:punct:]]")[[1]]
## words = words[words != ""]
## wordtab = table(words)
## return(wordtab)
## }

4、Multiple inputs

Our function can take more than one input

c 复制代码
# get.wordtab.from.url: get a word table from text on the web
# Inputs:
# - str.url: string, specifying URL of a web page 
# - split: string, specifying what to split on
# Output: word table, i.e., vector with counts as entries and associated
#   words as names

get.wordtab.from.url = function(str.url, split) {
  lines = readLines(str.url)
  text = paste(lines, collapse=" ")
  words = strsplit(text, split=split)[[1]]
  words = words[words != ""]
  table(words)
}
  • Inputs:
  • str.url: string, specifying URL of a web page
  • split: string, specifying what to split on
  • Output: word table, i.e., vector with counts as entries and associated words as names

5、Default inputs

Our function can also specify default values for the inputs (if the user doesn't specify an input in the function call, then the default value is used)

c 复制代码
# get.wordtab.from.url: get a word table from text on the web
# Inputs:
# - str.url: string, specifying URL of a web page 
# - split: string, specifying what to split on. Default is the regex pattern
#   "[[:space:]]|[[:punct:]]"
# - convert2lower: Boolean, TRUE if words should be converted to lower case before
#   the word table is computed. Default is TRUE
# Output: word table, i.e., vector with counts as entries and associated
#   words as names

get.wordtab.from.url = function(str.url, split="[[:space:]]|[[:punct:]]", 
                                convert2lower=TRUE) {
  lines = readLines(str.url)
  text = paste(lines, collapse=" ")
  words = strsplit(text, split=split)[[1]]
  words = words[words != ""]
  # Convert to lower case, if we're asked to
  if (convert2lower) words = tolower(words)
  table(words)
}

二、Return values and side effects

1、Returning more than one thing

R doesn't let your function have multiple outputs, but you can return a list

When creating a function in R, though you cannot return more than one output, you can return a list. This (by definition) can contain an arbitrary number of arbitrary objects

  • Inputs :
    • str.url: string, specifying URL of a web page
    • split: string, specifying what to split on. Default is the regex pattern "[[:space:]]|[[:punct:]]"
    • convert2lower: Boolean, TRUE if words should be converted to lower case before the word table is computed. Default is TRUE
    • keep.nums: Boolean, TRUE if words containing numbers should be kept in the word table. Default is FALSE
  • Output: list, containing word table, and then some basic numeric summaries
c 复制代码
get.wordtab.from.url = function(str.url, 
                                split="[[:space:]]|[[:punct:]]",
                                convert2lower=TRUE, keep.nums=FALSE) {
  lines = readLines(str.url)
  text = paste(lines, collapse=" ")
  words = strsplit(text, split=split)[[1]]
  words = words[words != ""]
  
  # Convert to lower case, if we're asked to
  if (convert2lower) {
    words = tolower(words)
  }
  
  # Get rid of words with numbers, if we're asked to
  if (!keep.nums) {
    words = grep("[0-9]", words, invert=TRUE, value=TRUE)
  }
  
  # Compute the word table
  wordtab = table(words)
  return(list(wordtab=wordtab,
              number.unique.words=length(wordtab),
              number.total.words=sum(wordtab),
              longest.word=words[which.max(nchar(words))]))
}
c 复制代码
# King's "I Have A Dream" speech 
king.wordtab = get.wordtab.from.url(
  "https://raw.githubusercontent.com/king.txt")
lapply(king.wordtab, head)

## $wordtab
## words
## a able again ago ahead alabama
## 37 8 2 1 1 3
##
## $number.unique.words
## [1] 528
##
## $number.total.words
## [1] 1631
##
## $longest.word
## [1] "discrimination"

2、Side effects

A side effect of a function is something that happens as a result of the function's body, but is not returned. Examples:

  • Printing something out to the console
  • Plotting something on the display
  • Saving an R data file, or a PDF, etc.

Example of side effect: plot

  • get.wordtab.from.url: get a word table from text on the web
  • Inputs :
    • str.url: string, specifying URL of a web page
    • split: string, specifying what to split on. Default is the regex pattern "[[:space:]]|[[:punct:]]"
    • convert2lower: Boolean, TRUE if words should be converted to lower case before the word table is computed. Default is TRUE
    • keep.nums: Boolean, TRUE if words containing numbers should be kept in the word table. Default is FALSE
    • plot.hist: Boolean, TRUE if a histogram of word lengths should be plotted as a side effect. Default is FALSE
  • Output: list, containing word table, and then some basic numeric summaries
c 复制代码
get.wordtab.from.url = function(str.url, split="[[:space:]]|[[:punct:]]",
                                convert2lower=TRUE, keep.nums=FALSE, plot.hist=FALSE) {
  lines = readLines(str.url)
  text = paste(lines, collapse=" ")
  words = strsplit(text, split=split)[[1]]
  words = words[words != ""]
  
  # Convert to lower case, if we're asked to
  if (convert2lower) words = tolower(words)
  
  # Get rid of words with numbers, if we're asked to
  if (!keep.nums) 
    words = grep("[0-9]", words, invert=TRUE, value=TRUE)
  
  # Plot the histogram of the word lengths, if we're asked to
  if (plot.hist) 
    hist(nchar(words), col="lightblue", breaks=0:max(nchar(words)),
         xlab="Word length")
  
  # Compute the word table
  wordtab = table(words)
  
  return(list(wordtab=wordtab,
              number.unique.words=length(wordtab),
              number.total.words=sum(wordtab),
              longest.word=words[which.max(nchar(words))]))
}
c 复制代码
# King's speech
king.wordtab = get.wordtab.from.url(
  str.url="https://raw.githubusercontent.com/mxcai/BIOS5801/main/data/king.txt",
  plot.hist=TRUE)

三、Environments and design

1、Environment: what the function can see and do

  • Each function generates its own environment
  • Variable names in function environment override names in the global environment
  • Internal environment starts with the named arguments
  • Assignments inside the function only change the internal environment
  • Variable names undefined in the function are looked for in the global environment

2、Environment examples

  • Variable names here override names in the global environment

    • y is 2 in the global environment
    • y is 10 in the function environment, and only exists when the function is under execution
  • Variable assignments inside the function environment would (generally) not change the variable in the global environment

    • x remains to be 1 in the global environment
c 复制代码
x <- 1
y <- 2
addone = function(y) { 
  x = 1+y
  x 
}
addone(10)
## [1] 11

y
## [1] 2

x
## [1] 1
  • Variable names undefined in the function are looked for in the global environment
c 复制代码
circle.area = function(r) { pi*r^2 }
circle.area(1:3)
## [1] 3.141593 12.566371 28.274334

true.pi = pi # to back up the sanity
pi = 3 
circle.area(1:3)
## [1] 3 12 27

pi = true.pi # Restore sanity
circle.area(1:3)
## [1] 3.141593 12.566371 28.274334
相关推荐
我真的不会C9 分钟前
QT窗口相关控件及其属性
开发语言·qt
CodeCraft Studio9 分钟前
Excel处理控件Aspose.Cells教程:使用 Python 在 Excel 中进行数据验
开发语言·python·excel
火柴盒zhang15 分钟前
websheet之 编辑器
开发语言·前端·javascript·编辑器·spreadsheet·websheet
景天科技苑22 分钟前
【Rust】Rust中的枚举与模式匹配,原理解析与应用实战
开发语言·后端·rust·match·enum·枚举与模式匹配·rust枚举与模式匹配
时间之城25 分钟前
笔记:记一次使用EasyExcel重写convertToExcelData方法无法读取@ExcelDictFormat注解的问题(已解决)
java·spring boot·笔记·spring·excel
阿让啊28 分钟前
C语言中操作字节的某一位
c语言·开发语言·数据结构·单片机·算法
椰羊~王小美33 分钟前
LeetCode -- Flora -- edit 2025-04-25
java·开发语言
灏瀚星空34 分钟前
用Obsidian四个插件打造小说故事关联管理系统:从模板到图谱的全流程实践
经验分享·笔记·开源
一只可爱的小猴子1 小时前
2022李宏毅老师机器学习课程笔记
人工智能·笔记·机器学习
孞㐑¥1 小时前
C++11介绍
开发语言·c++·经验分享·笔记