I have the following data frame,

id    <- c(10, 12, 13, 14, 15)
x.a <- c(1, 1, 0, 0, 1)
x.b <- c(NA, NA, NA, 5, 4)
y.a <- c(0,0,0, NA, NA)
y.b <- c(0, 0, 1, 1, NA)

df <- data.frame(id, x.a, x.b, y.a, y.b)

df 

> df
  id x.a x.b y.a y.b
1 10   1  NA   0   0
2 12   1  NA   0   0
3 13   0  NA   0   1
4 14   0   5  NA   1
5 15   1   4  NA  NA

I want to summarise across columns (e.g. min, max). This is what I am doing,

df %>% 
  group_by(id) %>% 
  summarise(across(ends_with("a"), (x) max(x, na.rm = TRUE))) %>% 
  summarise(across(ends_with("b"), (x) min(x, na.rm = TRUE)))

This is giving me an error message like this,

Warning message:
There were 2 warnings in `summarise()`.
The first warning was:
ℹ In argument: `across(ends_with("a"), max, na.rm = TRUE)`.
ℹ In group 4: `id = 14`.
Caused by warning in `fn()`:
! no non-missing arguments to max; returning -Inf
ℹ Run dplyr::last_dplyr_warnings() to see the 1 remaining warning.

Any idea what am I doing wrong here?