{ "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "# 函数操作\n", "\n", "本文介绍 R 中的控制语句（条件 if/switch 与循环 for/while），抛出警告与异常（stop()/warning()/message()），以及如何自编写函数、如何把编写函数放入启动环境中。\n", "\n", "## 条件语句\n", "\n", "### if 语句\n", "\n", "R 中的 if 语句有三种形式：\n", "\n", "- If (cond) state \n", "- If (cond) yes-state else no-state\n", "- Ifelse (cond, yes-state, no-state)" ] }, { "cell_type": "code", "execution_count": 1, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[1] TRUE\n" ] } ], "source": [ "# if 语句\n", "if (2 > 1) {\n", " a <- TRUE\n", "}\n", "print(a)" ] }, { "cell_type": "code", "execution_count": 2, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[1] TRUE\n" ] } ], "source": [ "# if-else 语句\n", "if (2 != 1) {\n", " a <- TRUE\n", "} else {\n", " a <- False\n", "}\n", "print(a)" ] }, { "cell_type": "code", "execution_count": 3, "metadata": {}, "outputs": [ { "data": { "text/html": [ "TRUE" ], "text/latex": [ "TRUE" ], "text/markdown": [ "TRUE" ], "text/plain": [ "[1] TRUE" ] }, "metadata": {}, "output_type": "display_data" } ], "source": [ "# 三元选择器：ifelse()\n", "ifelse(2 != 1, a <- TRUE, a <- False)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "### switch 语句" ] }, { "cell_type": "code", "execution_count": 4, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[1] \"A\"\n", "[1] \"B\"\n", "[1] \"C\"\n" ] } ], "source": [ "dt <- c(\"a\", \"b\", \"c\")\n", "for (i in dt) {\n", " print(switch(i, a = \"A\", b = \"B\", c = \"C\"))\n", "}" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 循环语句\n", "\n", "之前在 [“数据管理”一文](ManageData.ipynb#函数式编程) 中介绍过函数式编程 apply()。如果可能，请尽量使用函数式编程，而不是使用循环语句。\n", "\n", "### for 语句\n", "\n", "在 switch() 中已经展示了 for 语句的用法。\n", "\n", "### while 语句" ] }, { "cell_type": "code", "execution_count": 5, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[1] 0\n", "[1] 1\n", "[1] 2\n" ] } ], "source": [ "i <- 0\n", "while (i < 3) {\n", " print(i)\n", " i <- i + 1\n", "}" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 自编写函数\n", "\n", "R 中的函数声明与其他语言并没有什么不同：" ] }, { "cell_type": "code", "execution_count": 6, "metadata": {}, "outputs": [ { "data": { "text/html": [ "\n", "\n", "\n", "\t\n", "\t\n", "\t\n", "\n", "
XYSUM
145
257
369
\n" ], "text/latex": [ "\\begin{tabular}{r|lll}\n", " X & Y & SUM\\\\\n", "\\hline\n", "\t 1 & 4 & 5\\\\\n", "\t 2 & 5 & 7\\\\\n", "\t 3 & 6 & 9\\\\\n", "\\end{tabular}\n" ], "text/markdown": [ "\n", "X | Y | SUM | \n", "|---|---|---|\n", "| 1 | 4 | 5 | \n", "| 2 | 5 | 7 | \n", "| 3 | 6 | 9 | \n", "\n", "\n" ], "text/plain": [ " X Y SUM\n", "1 1 4 5 \n", "2 2 5 7 \n", "3 3 6 9 " ] }, "metadata": {}, "output_type": "display_data" } ], "source": [ "DfSum <- function(x, is.print=FALSE) {\n", " # Compute the sum of all columns and put the results into SUM column.\n", " #\n", " # Args: \n", " # x: Any data.frame object.\n", " # is.print: if TRUE, print the new data.frame to the screen\n", " #\n", " # Returns:\n", " # A data.frame combined by the original one and the SUM column.\n", " if (class(x) != \"data.frame\") {\n", " stop(\"Require data.frame input.\")\n", " }\n", " x$SUM <- apply(x, 1, sum)\n", " if (is.print)\n", " print(x)\n", " return(x)\n", "}\n", "\n", "dt <- data.frame(X=c(1:3), Y=c(4:6))\n", "DfSum(dt)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## R 启动环境：Startup\n", "\n", "我们常常把函数写在 R 文件中，然后在需要使用时用 source() 命令引用它。你可以配置 R 的相关配置文件（R 的安装目录下 etc/Rprofile.site 文件），使得你可以在任何 R 项目中方便地调用本地自编写的函数。\n", "\n", "你可以在其中创建一个名为 .First() 的函数，作为**每个 R 会话的启动函数**。一个例子：\n", "\n", "```r\n", ".First() <- function() {\n", " library(Hmisc) # 加载 Hmisc 包\n", " source(\"c:/R-files/myfunctions.R\")\n", "}\n", "```\n", "\n", "同理可以设置的还有关闭函数，叫做 .Last()。例如自动保存历史文件：\n", "\n", "```r\n", ".Last() <- function() {\n", " history.name <- paste(paste(\"AutoSave\", Sys.Date(), strsplit(date(), \" \")[[1]][4], sep=\"-\"), \".Rhistory\", sep=\"\")\n", " savehistory(paste(getwd(), history.name))\n", "}\n", "```\n", "\n", "可以通过 help(Startup) 查看更多的内容。" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 抛出异常\n", "\n", "你可能注意到了 stop() 函数，它在自编写函数中用于停止编译，可能会被经常用到。\n", "\n", "- stop(): 停止执行并报错。\n", "- warning()：错误提示。\n", "- message()：诊断信息提示。\n", "\n", "我们可以测试刚才编写的 DfSum 函数中使用的 stop()，输入一个不符合输入要求的参数：" ] }, { "cell_type": "code", "execution_count": 7, "metadata": {}, "outputs": [ { "ename": "ERROR", "evalue": "Error in DfSum(\"abc\"): Require data.frame input.\n", "output_type": "error", "traceback": [ "Error in DfSum(\"abc\"): Require data.frame input.\nTraceback:\n", "1. DfSum(\"abc\")", "2. stop(\"Require data.frame input.\") # at line 11 of file " ] } ], "source": [ "DfSum(\"abc\")" ] } ], "metadata": { "kernelspec": { "display_name": "R", "language": "R", "name": "ir" }, "language_info": { "codemirror_mode": "r", "file_extension": ".r", "mimetype": "text/x-r-source", "name": "R", "pygments_lexer": "r", "version": "4.0.0" }, "toc": { "base_numbering": 1, "nav_menu": {}, "number_sections": true, "sideBar": true, "skip_h1_title": false, "title_cell": "Table of Contents", "title_sidebar": "Contents", "toc_cell": false, "toc_position": {}, "toc_section_display": true, "toc_window_display": false } }, "nbformat": 4, "nbformat_minor": 2 }