合并后维护数据框列的属性

Question

似乎merge导致数据框的列丢失其属性:

attr(mtcars$mpg, "units") <- "miles.per.gallon"
new.df <- data.frame(gear=3:5, my.opinion=c("not enough", "just right", "too many"))
merged.df <- merge(new.df, mtcars)

attr(merged.df$mpg, "units")回报NULL.

有没有办法merge保存列的属性？

(解决方法是在合并之前查询每个数据框的每一列的属性,然后在合并之后重新分配它们.但这看起来不够优雅.)

Answer 1

如果你不介意使用dplyr,这个似乎工作.

你的数据:

attr(mtcars$mpg, "units") <- "miles.per.gallon"
new.df <- data.frame(gear=3:5, my.opinion=c("not enough", "just right", "too many"))

> attr(mtcars$mpg, "units")
[1] "miles.per.gallon"

来自dplyr的函数inner_join.

inner.df<-dplyr::inner_join(new.df, mtcars,"gear")

结果数据框如下:

> inner.df
    gear my.opinion  mpg cyl  disp  hp drat    wt  qsec vs am carb
1     3 not enough 21.4   6 258.0 110 3.08 3.215 19.44  1  0    1
2     3 not enough 18.7   8 360.0 175 3.15 3.440 17.02  0  0    2
3     3 not enough 18.1   6 225.0 105 2.76 3.460 20.22  1  0    1
4     3 not enough 14.3   8 360.0 245 3.21 3.570 15.84  0  0    4
5     3 not enough 16.4   8 275.8 180 3.07 4.070 17.40  0  0    3
6     3 not enough 17.3   8 275.8 180 3.07 3.730 17.60  0  0    3
7     3 not enough 15.2   8 275.8 180 3.07 3.780 18.00  0  0    3
8     3 not enough 10.4   8 472.0 205 2.93 5.250 17.98  0  0    4
9     3 not enough 10.4   8 460.0 215 3.00 5.424 17.82  0  0    4
10    3 not enough 14.7   8 440.0 230 3.23 5.345 17.42  0  0    4
11    3 not enough 21.5   4 120.1  97 3.70 2.465 20.01  1  0    1
12    3 not enough 15.5   8 318.0 150 2.76 3.520 16.87  0  0    2
13    3 not enough 15.2   8 304.0 150 3.15 3.435 17.30  0  0    2
14    3 not enough 13.3   8 350.0 245 3.73 3.840 15.41  0  0    4
15    3 not enough 19.2   8 400.0 175 3.08 3.845 17.05  0  0    2
16    4 just right 21.0   6 160.0 110 3.90 2.620 16.46  0  1    4
17    4 just right 21.0   6 160.0 110 3.90 2.875 17.02  0  1    4
18    4 just right 22.8   4 108.0  93 3.85 2.320 18.61  1  1    1
19    4 just right 24.4   4 146.7  62 3.69 3.190 20.00  1  0    2
20    4 just right 22.8   4 140.8  95 3.92 3.150 22.90  1  0    2
21    4 just right 19.2   6 167.6 123 3.92 3.440 18.30  1  0    4
22    4 just right 17.8   6 167.6 123 3.92 3.440 18.90  1  0    4
23    4 just right 32.4   4  78.7  66 4.08 2.200 19.47  1  1    1
24    4 just right 30.4   4  75.7  52 4.93 1.615 18.52  1  1    2
25    4 just right 33.9   4  71.1  65 4.22 1.835 19.90  1  1    1
26    4 just right 27.3   4  79.0  66 4.08 1.935 18.90  1  1    1
27    4 just right 21.4   4 121.0 109 4.11 2.780 18.60  1  1    2
28    5   too many 26.0   4 120.3  91 4.43 2.140 16.70  0  1    2
29    5   too many 30.4   4  95.1 113 3.77 1.513 16.90  1  1    2
30    5   too many 15.8   8 351.0 264 4.22 3.170 14.50  0  1    4
31    5   too many 19.7   6 145.0 175 3.62 2.770 15.50  0  1    6
32    5   too many 15.0   8 301.0 335 3.54 3.570 14.60  0  1    8

属性被保留的位置:

> attr(inner.df$mpg, "units")
[1] "miles.per.gallon"