汇总变量并将结果添加到现有数据框中

Question

I need to group by "id_group" and find the median price, and then add this in the existing df.

summarise will help us finding the median price after group_by but how do I add this new variable to the existing df? mutate might also not help as it will not summarise but keep repeating the entries of the grouping variable.

I tried ave() too but didn't help. Any other solution?

Existing data frame

1. id  group  value1 value2
    1.   a      10       1.2 
    2.   a      20       1.3
    3.   b      100      5.1 
    4.   b      200      5.4

Output needed:

 1. id  group  value  grp.median.values1 grp.median.values2 
    1.   a      10     10                  1.2
    2.   b      100    100                 5.1

Answer 1

Mutating median after original values does not make sense. The idea of summarise() is to collapse many values to their representatives.

Your final output example just prints one value for each group (first value1 and first value2 in a / first value1 and first value2 in b ).
I think this means nothing.

Collapse many values down to a single summary ( summarise() ).

[ http://r4ds.had.co.nz/transform.html#introduction-2][1]

I think you have already know how:

library(tidyverse)

df <-
  tribble(
    ~id, ~group, ~value1, ~value2,
    "1.", "a", 10, 1.2,
    "2.", "a", 20, 1.3,
    "3.", "b", 100, 5.1,
    "4.", "b", 200, 5.4,
  )

df %>%
  group_by(group) %>%
  summarise_if(is.numeric, median)

## # A tibble: 2 x 3
##   group value1 value2
##   <chr>  <dbl>  <dbl>
## 1 a         15   1.25
## 2 b        150   5.25