dplyr基于某些条件创建新列

Question

我有以下df：

df<-data.frame(geo_num=c(11,12,22,41,42,43,77,71),
               cust_id=c("A","A","B","C","C","C","D","D"),
               sales=c(2,3,2,1,2,4,6,3))
> df
  geo_num cust_id sales
1      11       A     2
2      12       A     3
3      22       B     2
4      41       C     1
5      42       C     2
6      43       C     4
7      77       D     6
8      71       D     3

需要创建一个新列“geo_num_new”，该列对“cust_id”中的每个组都有来自“geo_num”的第一个值，如下所示：

> df_new
  geo_num cust_id sales geo_num_new
1      11       A     2          11
2      12       A     3          11
3      22       B     2          22
4      41       C     1          41
5      42       C     2          41
6      43       C     4          41
7      77       D     6          77
8      71       D     3          77

谢谢。

Answer 1

我们可以在按“cust_id”进行分组后使用first。单个值将用于整个分组。

library(dplyr)
df <- df %>% 
    group_by(cust_id) %>%
    mutate(geo_num_new = first(geo_num)) %>%
    ungroup

-ouptut

df
# A tibble: 8 x 4
  geo_num cust_id sales geo_num_new
    <dbl> <chr>   <dbl>       <dbl>
1      11 A           2          11
2      12 A           3          11
3      22 B           2          22
4      41 C           1          41
5      42 C           2          41
6      43 C           4          41
7      77 D           6          77
8      71 D           3          77

或者使用data.table

library(data.table)
setDT(df)[, geo_num_new := first(geo_num), by = cust_id]

或使用base R

df$geo_num_new <- with(df, ave(geo_num, cust_id, FUN = function(x) x[1]))

或使用collapse选项

library(collapse)
tfm(df, geo_num_new = ffirst(geo_num, g = cust_id, TRA = "replace"))
  geo_num cust_id sales geo_num_new
1      11       A     2          11
2      12       A     3          11
3      22       B     2          22
4      41       C     1          41
5      42       C     2          41
6      43       C     4          41
7      77       D     6          77
8      71       D     3          77