Had a case like this. Tried to convert "mtcars" class from data.frame to data.table.
有这样的情况。试图将“mtcars”类从data.frame转换为data.table。
"mtcars" data:
“mtcars”数据：
> mtcars
mpg cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
Original class is "data.frame".
原始类是“data.frame”。
> str(mtcars)
'data.frame': 32 obs. of 11 variables:
$ mpg : num 21 21 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 ...
$ cyl : num 6 6 4 6 8 6 8 4 4 6 ...
$ disp: num 160 160 108 258 360 ...
$ hp : num 110 110 93 110 175 105 245 62 95 123 ...
$ drat: num 3.9 3.9 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 ...
$ wt : num 2.62 2.88 2.32 3.21 3.44 ...
$ qsec: num 16.5 17 18.6 19.4 17 ...
$ vs : num 0 0 1 1 0 1 0 1 1 1 ...
$ am : num 1 1 1 0 0 0 0 0 0 0 ...
$ gear: num 4 4 4 3 3 3 3 4 4 4 ...
$ carb: num 4 4 1 1 2 1 4 2 2 4 ...
Convert to data.table. Found the Column for car brands are gone. Why? How to retain the column of brands?
转换为data.table。发现汽车品牌专栏已经不见了。为什么？如何保留品牌栏目？
> mtcars2 <- data.table(mtcars)
> mtcars2
mpg cyl disp hp drat wt qsec vs am gear carb
1: 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
2: 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
3: 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
Would like to have a data.table with final data format as below -- having a NEW column name "Brands" for the first column of brands. How to code to add the column "Brands" from the original "mtcars" dataset?
想拥有一个data.table，最终数据格式如下 - 第一列品牌的新名称为“Brands”。如何编码从原始“mtcars”数据集添加“品牌”列？
Brands mpg cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
1 个解决方案
#1
11
It's the rownames that are missing, not one of the columns.
这是缺少的rownames，而不是其中一个列。
If you want Brands as a column, the manual approach is:
如果您想将品牌作为专栏，那么手动方法是：
data.table(Brands = rownames(mtcars), mtcars)
Alternately:
交替：
data.table(mtcars, keep.rownames = TRUE)
However, this does not make the resulting data.table have the old rownames, it just makes a column for them, called "rn". This is in the documentation, ?data.table.
但是，这并不会使得结果data.table具有旧的rownames，它只为它们创建一个列，称为“rn”。这是在文档中，？data.table。
Alternately, modify the table in place, for DF = mtcars:
或者，为DF = mtcars修改表格：
setDT(DF, keep.rownames = "Brands")
Minor point: we cannot setDT(mtcars, ...), since mtcars is a built-in table.
小点：我们不能设置DT（mtcars，...），因为mtcars是一个内置表。
#1
11
It's the rownames that are missing, not one of the columns.
这是缺少的rownames，而不是其中一个列。
If you want Brands as a column, the manual approach is:
如果您想将品牌作为专栏，那么手动方法是：
data.table(Brands = rownames(mtcars), mtcars)
Alternately:
交替：
data.table(mtcars, keep.rownames = TRUE)
However, this does not make the resulting data.table have the old rownames, it just makes a column for them, called "rn". This is in the documentation, ?data.table.
但是，这并不会使得结果data.table具有旧的rownames，它只为它们创建一个列，称为“rn”。这是在文档中，？data.table。
Alternately, modify the table in place, for DF = mtcars:
或者，为DF = mtcars修改表格：
setDT(DF, keep.rownames = "Brands")
Minor point: we cannot setDT(mtcars, ...), since mtcars is a built-in table.
小点：我们不能设置DT（mtcars，...），因为mtcars是一个内置表。