June 2020
Beginner to intermediate
522 pages
9h 6m
Chinese
Content preview from R 语言经典实例（原书第 2 版）
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3.4.3 讨论
history 函数能显示最近使用的命令。在 RStudio 中，history 函数将打开“历史记
录 ”（ History）窗格。如果你在 RStudio 之外运行 R，history 函数会显示最近的 25 行
命令，当然你可以要求显示更多的历史命令：
history(100) # Show 100 most recent lines of history
history(Inf) # Show entire saved history
在 RStudio 中，“历史记录” （ History）窗格按时间顺序显示过去命令的详尽列表，最新
列表位于列表底部。你可以使用光标突出显示过去的命令，然后单击“ To Console”或
“ To Source ”将过去的命令分别复制到控制台或代码编辑器中。当你完成交互式数据分
析并决定将某些过去的步骤保存到源文件以供以后使用时，这将非常方便。
在控制台中，你只需按向上箭头向后滚动输入即可查看历史记录，找回之前的命令，每
按一次显示一行。
即使你已退出 R 或 RStudio，也可以查看命令历史记录。R 将历史记录保存在工作目录
中名为
.Rhistory
的文件中。使用文本编辑器打开文件，然后滚动到底部，你会看到最近
输入的命令。
3.5 保存先前命令产生的结果
3.5.1 问题
在 R 中键入一个表达式得到一个计算结果，却忘了将该结果保存到一个变量中。
3.5.2 解决方案
R 中有个一个名为 .Last.value 的特殊变量，它存储最近一个计算出的表达式值。在 ...
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