Nested pipe chain in dplyr / left_join

Though this isn't an answer to my question (Onyambo provided that!), I wanted to share that I found an alternative way to accomplish the same thing. Basically you use group_by() and nest() to squish the tibble and get the repeated vars out of the way, do the lag, and then unnest().

df %>% 
  group_by(Team, Date) %>% 
  nest() %>% 
  mutate(Date_Lagged = lag(Date)) %>% 
  unnest()
#> # A tibble: 11 x 4
#>    Team  Date       Date_Lagged Points
#>    <fct> <fct>      <fct>        <dbl>
#>  1 A     2016-05-10 <NA>             1
#>  2 A     2016-05-10 <NA>             4
#>  3 A     2016-05-10 <NA>             3
#>  4 A     2016-05-10 <NA>             2
#>  5 B     2016-05-12 2016-05-10       1
#>  6 B     2016-05-12 2016-05-10       5
#>  7 B     2016-05-12 2016-05-10       6
#>  8 C     2016-05-15 2016-05-12       1
#>  9 C     2016-05-15 2016-05-12       2
#> 10 D     2016-05-30 2016-05-15       3
#> 11 D     2016-05-30 2016-05-15       9

Created on 2018-06-14 by the reprex package (v0.2.0).

For your code to work, you will need a curly brace around the y argument as shown below

  df %>% left_join(x = ., y = {.} %>% 
                   distinct(Team, Date) %>% 
                   mutate(Date_Lagged = lag(Date)))

Joining, by = c("Team", "Date")
   Team       Date Points Date_Lagged
1     A 2016-05-10      1        <NA>
2     A 2016-05-10      4        <NA>
3     A 2016-05-10      3        <NA>
4     A 2016-05-10      2        <NA>
5     B 2016-05-12      1  2016-05-10
6     B 2016-05-12      5  2016-05-10
7     B 2016-05-12      6  2016-05-10
8     C 2016-05-15      1  2016-05-12
9     C 2016-05-15      2  2016-05-12
10    D 2016-05-30      3  2016-05-15
11    D 2016-05-30      9  2016-05-15

oe you can just do

df %>% left_join(df%>% 
                   distinct(Team, Date) %>% 
                   mutate(Date_Lagged = lag(Date)))

If you don't mind swapping pipe nesting for function nesting, this accomplishes your goal:

df %>% left_join(mutate(distinct(., Team, Date), Date_Lagged = lag(Date)))

output:

Joining, by = c("Team", "Date")
   Team       Date Points Date_Lagged
1     A 2016-05-10      1        <NA>
2     A 2016-05-10      4        <NA>
3     A 2016-05-10      3        <NA>
4     A 2016-05-10      2        <NA>
5     B 2016-05-12      1  2016-05-10
6     B 2016-05-12      5  2016-05-10
7     B 2016-05-12      6  2016-05-10
8     C 2016-05-15      1  2016-05-12
9     C 2016-05-15      2  2016-05-12
10    D 2016-05-30      3  2016-05-15
11    D 2016-05-30      9  2016-05-15