merging two data frames by column, but only one column in R

Question

I have two data frames of this form:

A

code  population index
1        400       5
...

B

code  rate index
1      50    5
...

I want to merge B in A by code, but I want only to merge rate. Expected output:

C

code  population  rate  index
1      400         50     5
...

How to do that in R?

Do you want to merge on `code` or `index`? (It's hard to tell because they are the same in your sample data, so merging on one or both is the same). — Gregor Thomas, Nov 16 '20 at 17:50
But the general answer is subset the columns from `B` that you want to merge, e.g., `merge(A, B)` merges `rate` based on `code` and `index` (all common columns); `merge(A, B[c("code", "rate")])` merges `rate` based on `code` - we dropped `index` from `B` before the merge. — Gregor Thomas, Nov 16 '20 at 17:51
@GregorThomas I just want to merge B column "rate" in A based on code not index. — v_head, Nov 16 '20 at 17:55

score 0 · Answer 1 · answered Nov 16 '20 at 17:55

Here is an option using dplyr. Here is some information on how to provide a proper reproducible example.

library(tibble)
library(dplyr)

df_a <- tibble(
  code = 1,
  population = 400,
  index = 5
)

df_b <- tibble(
  code = 1,
  rate = 50,
  index = 5
)

df_a %>% 
  inner_join(df_b, by = "code") %>% 
  select(code, population, rate, index.x) %>% 
  rename(index = index.x)

#> # A tibble: 1 x 4
#>    code population  rate index
#>   <dbl>      <dbl> <dbl> <dbl>
#> 1     1        400    50     5

^{Created on 2020-11-16 by the reprex package (v0.3.0)}

Ok, but @Gregor Thomas answer is the simplest: merge(A, B[c("code", "rate")]) — v_head, Nov 16 '20 at 18:01

merging two data frames by column, but only one column in R

1 Answers1