How can values from the same column that are assigned to the same group be placed in separate columns in R?

Question

Let's say I have a given dataframe df, that looks like this:

df
   Group <- c("A","B","C","D","E","B","D","E")
   Value <- c(2,3,2,2,1,5,4,4)
    
df <- data.frame(Group, Value)

df
  Group Value
1    A     2
2    B     3
3    C     2
4    D     2
5    E     1
6    B     5
7    D     4
8    E     4

I want to look for duplicates in Group and then put the two Values that go with that Group in seperate columns. I also want to remove any row or Group with only one Value (per group).

So the resulting dataframe in this case would look like this:

new_df
  Group Value1 Value2
1    B      3      5
2    D      2      4
3    E      1      4

I would be very happy, if someone could help me with this!

Thank you very much in advance!

Answer 1

The basic reshaping component of this is well-informed by Reshape multiple value columns to wide format, though for those steps to work we need to bring in a "counter" column to filter and expand on.

dplyr and tidyr

library(dplyr)
library(tidyr) # pivot_wider
df %>%
  group_by(Group) %>%
  mutate(rn = paste0("Value", row_number())) %>%
  filter(n() > 1) %>%
  ungroup() %>%
  pivot_wider(Group, names_from = rn, values_from = Value)
# # A tibble: 3 x 3
#   Group Value1 Value2
#   <chr>  <dbl>  <dbl>
# 1 B          3      5
# 2 D          2      4
# 3 E          1      4

base R and reshape2

df$rn <- paste0("Value", ave(seq_len(nrow(df)), df$Group, FUN = seq_along))
subset(df, ave(df$Group, df$Group, FUN = length) > 1) |>
  reshape2::dcast(Group ~ rn, value.var = "Value")
#   Group Value1 Value2
# 1     B      3      5
# 2     D      2      4
# 3     E      1      4

Answer 2

Another possible solution, based on tidyverse:

library(tidyverse)

df %>%
  group_by(Group) %>%
  filter(n() != 1) %>%
  group_split() %>%
  map_dfr(~ pivot_wider(mutate(.x, name = str_c("Value", 1:n())),
    Group, values_from = "Value"))

#> # A tibble: 3 × 3
#>   Group Value1 Value2
#>   <chr>  <dbl>  <dbl>
#> 1 B          3      5
#> 2 D          2      4
#> 3 E          1      4