r - 将 View 与 data.frame 子集结合使用会添加 row.names 列

Question

我创建两个子集(data.frames)，如下所示:

sms_raw_train <- sms_raw[1:4169, ]
sms_raw_test <- sms_raw[4170:5559, ]

第一个 sms_raw_train 如下所示:

    type    text
1   ham Hope you are having a good week. Just checking in
2   ham K..give back my thanks.
3   ham Am also doing in cbe only. But have to pay.

第二个，sms_raw_test，看起来像这样:

    row.names   type    text
1   4170    ham I'm coming home 4 dinner.
2   4171    ham Come by our room at some point so we can iron out the plan for this weekend
3   4172    ham Its sunny in california. The weather's just cool

如您所见，它添加了一个 row.names 列。但是，如果我这样做:

> str(sms_raw_test[1:3, ])
'data.frame':   3 obs. of  2 variables:
 $ type: Factor w/ 2 levels "ham","spam": 1 1 1
 $ text: chr  "I'm coming home 4 dinner." "Come by our room at some point so we can iron out the plan for this weekend" "Its sunny in california. The weather's just cool"

该列实际上并不存在。

本专栏的目的是什么？为什么将其添加到 View(sms_raw_train) 中？

Answer 1

View 正在添加该列以进行显示。正如您所看到的，它实际上并不存在于子集中。

来自帮助(查看):

If there are row names on the data frame that are not 1:nrow, they are displayed in a separate first column called row.names.

sms_raw_data 的行名称(大概是)4170:5559。

sms_raw_train 的行名称是 1:nrow，因此这种行为在那里并不明显。