Is there a way to append values of columns from 2 different data frames

Question

I have two data frames
df1:

DAT1 DAT3     DAT4    ...
 1   this is  this is
 2   this is  this is
 3   this is  this is

df2:

DAT1 DAT3       DAT4      ... 
 1   a comment  a comment
 2   a comment  a comment
 3   a comment  a comment

I want to find a way to append the second dataframe columns (I know both the name and the position of the columns I need to append)to the first one and obtain an updated version of the first one that has:
df3:

DAT1 DAT3               DAT4               ... 
 1   this is a comment  this is a comment  
 2   this is a comment  this is a comment
 3   this is a comment  this is a comment

The thing is that the real dataframes have many rows and columns, so a for() loop would be really inefficient.

@LyzandeR in theory yes. (Have not seen a case where that doesn't happen) — Aaron Parrilla
– Aaron Parrilla, Commented Jul 10, 2019 at 9:47

Ronak Shah · Accepted Answer · 2019-07-10 09:57:39Z

2

We can use Map

cols <- c("DAT3", "DAT4")
df3 <- df1
df3[cols] <- Map(paste, df1[cols], df2[cols])

df3
#  DAT1              DAT3              DAT4
#1    1 this is a comment this is a comment
#2    2 this is a comment this is a comment
#3    3 this is a comment this is a comment

answered Jul 10, 2019 at 9:57

Ronak Shah

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akrun · Accepted Answer · 2019-07-10 13:23:32Z

2

We can use base R without looping

cols <- c("DAT3", "DAT4")     
df3 <- df1
df3[cols] <-matrix(paste(as.matrix(df1[-1]), as.matrix(df2[-1])), nrow = nrow(df1))
df3
#  DAT1              DAT3              DAT4
#1    1 this is a comment this is a comment
#2    2 this is a comment this is a comment
#3    3 this is a comment this is a comment

data

df1 <- structure(list(DAT1 = 1:3, DAT3 = c("this is", "this is", "this is"
), DAT4 = c("this is", "this is", "this is")), class = "data.frame",
row.names = c(NA, 
-3L))

df2 <- structure(list(DAT1 = 1:3, DAT3 = c("a comment", "a comment", 
"a comment"), DAT4 = c("a comment", "a comment", "a comment")),
   class = "data.frame", row.names = c(NA, 
-3L))

edited Jul 10, 2019 at 13:23

answered Jul 10, 2019 at 13:18

akrun

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Comments

LyzandeR · Accepted Answer · 2019-07-10 09:54:31Z

1

If your data is ordered, I would do something like this:

#initiate the data.frame with the id
df3 <- data.frame(DAT1 = df1$DAT1)

#then run a for-loop with the names you know you need to concatenate
for (i in c('DAT3', 'DAT4')) {
  df3[[i]] <- paste(df1[[i]], df2[[i]])
}

The for-loop iterates over the names only. The core of the code is paste which is vectorised and fast. So, you won't face any speed issues

df3
#  DAT1              DAT3              DAT4
#1    1 this-is a-comment this-is a-comment
#2    2 this-is a-comment this-is a-comment
#3    3 this-is a-comment this-is a-comment

answered Jul 10, 2019 at 9:54

LyzandeR

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Jason Mathews · Accepted Answer · 2019-07-10 09:56:20Z

0

a dplyr version

df1 %>% inner_join(df2, by = "DAT1") %>% rowwise() %>%
  mutate(DAT3 = paste(DAT3.x, DAT3.y, collapse = " "),
         DAT4 = paste(DAT4.x, DAT4.y, collapse = " ")) %>%
  select(everything(), -contains("."))

OutPut

# A tibble: 3 x 3
   DAT1 DAT3              DAT4             
  <dbl> <chr>             <chr>            
1     1 this is a comment this is a comment
2     2 this is a comment this is a comment
3     3 this is a comment this is a comment

answered Jul 10, 2019 at 9:56

Jason Mathews

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