Question

我有一个old_df看起来像

old_df <- data.frame(Name = c("A", "A","A","B", "B", "C", "D", "E", "E"), 
             Value = c(1, 1, 1, 2, 2, 3, 4, 5, 5))

我想通过将Name保留在新数据中来更新此old_df并使用新的更新值。

new <- data.frame(Name = c("A", "E",), 
             Value = c(100, 500))

新输出看起来像

Answer 1

您可以使用match并将来自不匹配值的NA替换为旧值，即

old_df$new_val <- new$Value[match(old_df$Name, new$Name)]
old_df$new_val[is.na(old_df$new_val)] <- old_df$Value[is.na(old_df$new_val)]

或使用 dplyr ，

library(dplyr)

old_df %>% 
 left_join(new, by = 'Name') %>% 
 mutate(Value.y = replace(Value.y, is.na(Value.y), Value.x[is.na(Value.y)]))

两者都给予，

   Name Value new_val
1    A     1     100
2    A     1     100
3    A     1     100
4    B     2       2
5    B     2       2
6    C     3       3
7    D     4       4
8    E     5     500
9    E     5     500

Answer 2

另一种选择是使用data.table

的联接

library(data.table)
setDT(old_df)[new,  Value := i.Value, on = .(Name)]
old_df
#   Name Value
#1:    A   100
#2:    A   100
#3:    A   100
#4:    B     2
#5:    B     2
#6:    C     3
#7:    D     4
#8:    E   500
#9:    E   500

通过匹配名称更新值

2 个答案: