使用與data.frame子View會將row.names列

Question

我創建兩個子集（data.frames）像這樣：

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

第一，sms_raw_train，看起來是這樣的：

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，sms_raw_test，看起來是這樣的：

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 

正如你所看到的，它增加了一個row.names柱。但是，如果我這樣做：

> 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" 

該列實際上並不存在。

本專欄的目的是什麼？爲什麼它被添加到View(sms_raw_train)？

Answer 1

View正在添加該列進行顯示。正如你所看到的，它並不在子集中。

從help(View)：

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. 

行名字sms_raw_data是（大概）4170:5559。

sms_raw_train的行名是1:nrow，所以這種行爲在那裏並不明顯。