Adding values from one column to another with missing values in the second column using R

Question

I want to add just some specific values from column z in dataframe df2 into dataframe df1 , but just for the id = 1 and id = 3.

I have already tried solutions with ifelse , but for the missing values that kind of solutions work for the first value, until find the first missing gap.

 df1$z <- ifelse((df1$id == df2$id), df2$z, 0)

Examples of the data:

 df1 <- read.table(text = "
 id  v    w   
 1   20   B
 3   30   T

     ", h = T)

 df2 <- read.table(text = "
 id  z   b  c  d  e  f  g  h  i  j
 1   100   z  w  e  r  y  w  u  y  q
 2   800   t  q  j  n  m  q  i  x  z
 3   700   f  e  q  b  a  i  e  p  w
 4   300   a  b  c  d  a  g  s  y  q"                 
                   , h = T)

Expected result:

  df1_add <- read.table(text = "
  id  v    w   z 
  1   20   B  100
  3   30   T  700
                ", h = T)

Answer 1

Let's use left_join() and select() from the dplyr package:

library(dplyr)

df1_add <- df1 %>%
  left_join(df2 %>% select(id, z))

df1_add

  id  v w   z
1  1 20 B 100
2  3 30 T 700

Answer 2

you can try this

df_add <- df1
df_add$z = df2[df2$id %in% c(1, 3), ]$z

Answer 3

我们可以使用来自base R merge

merge(df1, df2[c("id", "z")])