[R] Bindings for paste(collapse), str_c(collapse), and str_flatten()

[asfimport]

These are the aggregating versions of string concatenation—they combine values from a set of rows into a single value. 

The bindings for paste() and str_c() might be tricky to implement because when these functions are called with the coallapse argument unset, they do not aggregate.

In summarise() we need to be able to use scalar concatenation within aggregate concatenation, like this: 

starwars %>%
  filter(!is.na(hair_color) & !is.na(eye_color)) %>% 
  group_by(homeworld) %>% 
  summarise(hair_and_eyes = paste0(paste0(hair_color, "-haired and ", eye_color, "-eyed"), collapse = ", "))

Reporter: Ian Cook / @ianmcook

Related issues:

• [C++] String concatenate aggregate kernel (depends upon)

_{Note: This issue was originally created as ARROW-12711. Please see the migration documentation for further details.}

[asfimport]

Travis Lim:
@ianmcook Any updates on bindings for dplyr summarise with paste(collapse) or str_c(collapse) in upcoming releases?

A potential workaround was floated for Python here https://issues.apache.org/jira/browse/ARROW-12710 but having this in R would be a game changer, especially for NLP applications 🙏 🙏 🙏