Merging data frame

General
2

You can use dplyr::left_join()

library(dplyr)

# Sample data in a copy/paste friendly format,
# replace this with your own data frames
df1 <- data.frame(
  stringsAsFactors = FALSE,
                 A = c("a", "b", "c", "d", "e"),
                 B = c(23, 10, 8, 43, 29)
)

df2 <- data.frame(
  stringsAsFactors = FALSE,
       check.names = FALSE,
              `A'` = c("a", "c", "d"),
                 C = c(4, 9, 18)
)

# Relevant code
df1 %>% 
    left_join(df2, by = c("A" = "A'"))
#>   A  B  C
#> 1 a 23  4
#> 2 b 10 NA
#> 3 c  8  9
#> 4 d 43 18
#> 5 e 29 NA

Created on 2022-06-30 by the reprex package (v2.0.1)

Note: Next time please provide a proper REPRoducible EXample (reprex) illustrating your issue.