psagg {wrapr}

Pseudo aggregator.

Description

Take a vector or list and return the first element (pseudo-aggregation or projection). If the argument length is zero or there are different items throw in an error.

Usage

psagg(x, ..., strict = TRUE)

Arguments

x

should be a vector or list of items.

...

force later arguments to be passed by name

strict

logical, should we check value uniqueness.

Details

This function is useful in some split by column situations as a safe and legible way to convert vectors to scalars.

Value

x[[1]] (or throw if not all items are equal or this is an empty vector).

Examples

d <- data.frame(
  group = c("a", "a", "b"),
  stringsAsFactors = FALSE)
dl <- lapply(
  split(d, d$group),
  function(di) {
    data.frame(
      # note: di$group is a possibly length>1 vector!
      # pseudo aggregate it to the value that is
      # constant for each group, confirming it is constant.
      group_label = psagg(di$group),
      group_count = nrow(di),
      stringsAsFactors = FALSE
    )
  })
do.call(rbind, dl)