Want to learn how to use nest and pipe

[fanzheng0352]

I want to ask some question about pipe and nest.

df <- tibble(x = c(1, 1, 1, 2, 2, 3), y = 1:6, z = 6:1)
df_nest <- df %>% nest(data = c(y, z)) 
df_nest
map(.x = df_nest$data, .f = ~mean(.x$y,na.rm = TRUE))  ### how to change that with pipe
df_nest %>% map(.x = data, .f = ~mean(.x$y,na.rm =TRUE))  ###  why this could not work

thank you.

[andresrcs]

@fanzheng0352

map(.x = df_nest$data, .f = ~mean(.x$y,na.rm = TRUE))  ### how to change that with pipe

I think this is a better way to work with a nested data frame

library(tidyverse)

df <- tibble(x = c(1, 1, 1, 2, 2, 3),
             y = 1:6,
             z = 6:1)

df %>% 
    nest(data = c(y, z)) %>% 
    mutate(mean_y = map_dbl(.x = data, .f = ~mean(.x$y, na.rm = TRUE)))
#> # A tibble: 3 × 3
#>       x data             mean_y
#>   <dbl> <list>            <dbl>
#> 1     1 <tibble [3 × 2]>    2  
#> 2     2 <tibble [2 × 2]>    4.5
#> 3     3 <tibble [1 × 2]>    6

@fanzheng0352

df_nest %>% map(.x = data, .f = ~mean(.x$y,na.rm =TRUE)) ### why this could not work

But to answer this question, you need to use a placeholder, otherwise, you would be passing the entire nested data frame as the first argument for map().

df %>% 
    nest(data = c(y, z)) %>% 
    map(.x = .$data, .f = ~mean(.x$y,na.rm =TRUE)) 
#> [[1]]
#> [1] 2
#> 
#> [[2]]
#> [1] 4.5
#> 
#> [[3]]
#> [1] 6

[fanzheng0352]

Thank you. I would try to understand it. Thank you!