How do pipes work with purrr map() function and the "." (dot) symbol

cars %>% 
  select_if(is.numeric) %>% 
  map2(., names(.), 
       ~{ggplot(data_frame(var = .x), aes(var)) + 
           geom_histogram() + 
           labs(x = .y)                    })

# Alternate version
cars %>% 
  select_if(is.numeric) %>% 
  imap(.,
       ~{ggplot(data_frame(var = .x), aes(var)) + 
           geom_histogram() + 
           labs(x = .y)                    })

There's a few extra steps.

• Use map2 instead of map. The first argument is the dataframe you're passing it, and the second argument is a vector of the names of that dataframe, so it knows what to map over. (Alternately, imap(x, ...) is a synonym for map2(x, names(x), ...). It's an "index-map", hence "imap".).
• You then need to explicitly enframe your data, since ggplot only works on dataframes and coercible objects.
• This also gives you access to the .y pronoun to name the plots.

You aren't supposed to pass raw data to an aesthetic mapping. Instead you should dynamically build the data.frame. For example

cars %>% 
  select_if(is.numeric) %>% 
  map(~ggplot(data_frame(x=.), aes(x)) + geom_histogram())