R 问题：如何在不替换现有数据的情况下向列添加数据？

Question

So I have a basic table with empty column 1

df

ident col1
     1   NA
     2   NA
     3   NA
     4   NA

I have two other tables:

df1

  ident col1
     2  Yes
     3  Yes

df2

  ident col1
     1  No
     4  No

I am trying to add data from each df1 and df2 to the first table but when I add the second df2 data it replaces the current entires there that don't match with NA. So I wan't to add df1 data into col1 and then add df2 data into col1 by matching ident numbers and without replacing values in there.

Here is my code:

df$col1<- df1$col1[match(df$ident, df1$ident)]

and then I do the same for df2 but it replaces df1 data...

Any suggestions? Thanks

PS. My data is much more complicated than this, I just figured i would boil it down easier for ya.

Answer 1

You just need to do the match the other way around

df$col1[match(df1$ident, df$ident)] <- df1$col1
df$col1[match(df2$ident, df$ident)] <- df2$col1


df
#    ident col1
# 1:     1   No
# 2:     2  Yes
# 3:     3  Yes
# 4:     4   No

You can also do this with data.table update joins

library(data.table)
setDT(df)
df[, col1 := as.character(col1)]# may not be necessary (if data is already char)

df[df1, on = .(ident), col1 := i.col1]
df[df2, on = .(ident), col1 := i.col1]


df
#    ident col1
# 1:     1   No
# 2:     2  Yes
# 3:     3  Yes
# 4:     4   No