在 R 中使用 `plot` 时添加的随机数据 [英] Random data added when using `plot` in R

问题描述

我偶然遇到了这个，我不知道发生了什么.谁能解释一下?

I came across this by accident, and I have no idea what's going on. Can anyone explain this?

plot(iris$Petal.Length,iris$foobar)

产生这个:

即使没有 iris$foobar，甚至只是一个 foobar 对象.这个 y 轴数据来自哪里?我在另一个 data.frame 中遇到过这个问题，所以这不是 iris 独有的(实际上，我在 iris 上尝试过，看看我的其他 data.frame 是否有问题).为什么 x 轴被标记为索引"?

Even though there is no iris$foobar, or even just a foobar object. Where is this y-axis data coming from? I've encountered this with another data.frame, so this is not unique to iris (in fact, I tried it on iris to see if there was something amiss with my other data.frame). And how come the x-axis is labeled as "Index"?

版本数据:平台 x86_64-w64-mingw32
拱形 x86_64
操作系统 mingw32
系统 x86_64，mingw32
状态
大三
次要 4.3
2017年
11月
第 30 天
SVN 修订版 73796
语言 R
version.string R 版本 3.4.3 (2017-11-30)昵称吃风筝的树

Version data: platform x86_64-w64-mingw32
arch x86_64
os mingw32
system x86_64, mingw32
status
major 3
minor 4.3
year 2017
month 11
day 30
svn rev 73796
language R
version.string R version 3.4.3 (2017-11-30) nickname Kite-Eating Tree

loadedNamespaces()
 [1] "Rcpp"         "HistData"     "bindr"        "magrittr"    
 [5] "grDevices"    "tidyselect"   "munsell"      "wordcloud"   
 [9] "colorspace"   "R6"           "rlang"        "stringr"     
[13] "plyr"         "dplyr"        "tools"        "utils"       
[17] "grid"         "gtable"       "stats"        "datasets"    
[21] "yaml"         "lazyeval"     "assertthat"   "tibble"      
[25] "base"         "bindrcpp"     "purrr"        "RColorBrewer"
[29] "ggplot2"      "tidyr"        "graphics"     "glue"        
[33] "slam"         "stringi"      "compiler"     "pillar"      
[37] "methods"      "scales"       "lubridate"    "pkgconfig"   
[41] "Cairo" 

推荐答案

d$foobar 被 plot() 忽略，因为 iris$foobar 是 NULL.

d$foobar is being ignored by plot(), because iris$foobar is NULL.

它只是绘制花瓣长度，x 轴为索引.

It's simply plotting the petal length, with on the x-axis the index.

与 plot(iris$Petal.Length) 或 plot(iris$Petal.Length, NULL) 比较.

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