CODEWITHSUNDEEP
rgroup-byunique
mevaldt
mevaldt

Reputation: 31

Unique different rows per group

I have a data frame that looks like this

    DF <- data.frame(x=rep(c("A", "B", "C"), times=1, each=3),
            y=c(1,2,3))

which gives me

       x y
     1 A 1
     2 A 2
     3 A 3
     4 B 1
     5 B 2
     6 B 3
     7 C 1
     8 C 2
     9 C 3

In my original dataframe, each column represents a person. So I must match one single x for a single y, giving me something like

    x y
    A 1
    B 2
    C 3

In other words, I need y grouped by x, but the y must not be repeat along the dataframe.

Any ideas to help?

I really looked for it on stackoverflow, but couldn't find anything that would help me. Thank you!!

Upvotes: 1

Views: 109

Answers (1)

www
www

Reputation: 39154

A solution using dplyr, assuming that all groups have the same number of rows as the group numbers.

library(dplyr)

DF2 <- DF %>%
  mutate(Group_ID = group_indices(., x)) %>%
  group_by(x) %>%
  summarise(y = y[first(Group_ID)]) %>%
  ungroup()
DF2
# # A tibble: 3 x 2
#   x         y
#   <fct> <dbl>
# 1 A         1
# 2 B         2
# 3 C         3

Or we can use the following:

DF2 <- DF %>% filter(as.numeric(x) == y)
DF2
#   x y
# 1 A 1
# 2 B 2
# 3 C 3

This works because column x is factor. When we convert it to numeric, we can filter with the value in y directly.

Upvotes: 2

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