R的数据集mtcars中的第一列是什么? [英] What is about the first column in R's dataset mtcars?
问题描述
我想我缺少关于R的数据帧的基本概念。
I think I am missing a fundamental concept about R's data frames.
head(mtcars)
mpg cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1
Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1
Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2
Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1
这里的汽车名称。这是专栏吗?我不这样认为,因为我无法通过 mtcars [,1]
访问它们。而且没有列名称/标题。
The names of the cars here. Is this a column? I don't think so, because I am not able to access them via mtcars[,1]
. And there is no column name/header for it.
如何创建这样的数据框?我如何使用该特殊列,例如
How could I create a data frame like that? How could I use that special column e.g. to describe the data in a plot for example?
推荐答案
它们是行名,要访问它们,请使用:
They are row names, to access them use:
rownames(mtcars)
对于列名使用colnames,要查看行和列名称,我们可以使用:
For column names use colnames, to see both row and column names, we can use:
dimnames(mtcars)
要进行修改,例如第一行:
To modify, for example the first row:
rownames(mtcars)[1] <- "myNewName"
使用data.frame创建数据框时,行名分配了1:n数字。
When data frame is created with data.frame, row names are assigned with 1:n numbers.
mydata <- data.frame(x = 1:5)
然后我们可以修改它们:
Then we can modify them:
rownames(mydata) <- paste0("MyName", 1:5)
或者我们可以在创建data.frame时添加行名:
Or we can add rownames when creating the data.frame:
mydata <- data.frame(x = 1:5, row.names = paste0("MyName", 1:5))
否te:
行名不是很可靠,例如,请参见此帖子。 (这可能是主观意见,我可以通过将行名重新分配给列来避免它们)
Note: rownames are not very reliable, for example see this post. (this could be subjective opinion and I avoid them by reassigning rownames to columns)
data.table和dplyr软件包首选不包含它们。您始终可以将行名重新分配为以下列:
data.table and dplyr packages prefer not to have them. You can always reassign rownames into a columns as:
mydata$myNames <- rownames(mydata)
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