How to subset a data frame based on a column of another data frame

Question

(Updated) I have dataframe1 that looks like:

  A C D E F
1 c f x i e
2 d g i d d
3 e h p e e

and dataframe2:

  A B
1 c q
2 d m

Noted that dataframe2$A is a subset of dataframe1$A. How do I subset dataframe1 based on column A of dataframe2, and add ONLY column C of dataframe1 to dataframe2? I hope to get:

  A B C
1 c q f
2 d m g

What do you mean by "subset dataframe1 based on column A of dataframe2"? If `dataframe2$A` had been "c, z" instead, would you just want the c-row of `dataframe1`? Or is it always true that `dataframe2$A` is a subset of `dataframe1$A`? — Aaron Montgomery, Apr 08 '20 at 16:50
`merge(df1, df2)` in base R, `inner_join(df1, df2)` in `dplyr`. — Gregor Thomas, Apr 08 '20 at 16:55
Hi @AaronMontgomery Yes, dataframe2$A is a subset of dataframe1$A — shenTTT, Apr 08 '20 at 17:05

David Ranzolin · Accepted Answer · 2020-04-08T16:57:06.107

1

You can use inner_join from dplyr:

library(dplyr)

df1 <- data.frame(A = c("c", "d", "e"),
           C = c("f", "g", "h"))

df2 <- data.frame(A = c("c", "d"),
                  B = c("q", "m"))

inner_join(df1, df2)
#> Joining, by = "A"
#> Warning: Column `A` joining factors with different levels, coercing to
#> character vector
#>   A C B
#> 1 c f q
#> 2 d g m

^{Created on 2020-04-08 by the reprex package (v0.3.0)}

edited Apr 08 '20 at 16:57

answered Apr 08 '20 at 16:53

David Ranzolin

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I updated the answer with inner_join – David Ranzolin Apr 08 '20 at 16:57

How to subset a data frame based on a column of another data frame

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