Extract vector functions from dplyr

[hadley]

Window functions: lead/lag, rank etc Cumulative: cumany cumall Vectorised: if_else recode case_when near

[DavisVaughan]

vec_lag() and vec_lead() seem straightforward-ish from dplyr::lag and dplyr::lead

library(vctrs)
library(rlang)

vec_lag <- function (x, n = 1L) {
  vec_assert(x)

  n <- vec_cast(n, integer())
  vec_assert(n, size = 1L)

  if (n < 0L) {
    abort("`n` must be positive.")
  }

  if (n == 0L) {
    return(x)
  }

  size <- vec_size(x)

  n <- pmin(n, size)

  new <- vec_init(x, n)
  old <- vec_slice(x, seq_len(size - n))

  vec_c(new, old)
}

vec_lead <- function (x, n = 1L) {
  vec_assert(x)

  n <- vec_cast(n, integer())
  vec_assert(n, size = 1L)

  if (n < 0L) {
    abort("`n` must be positive.")
  }

  if (n == 0L) {
    return(x)
  }

  size <- vec_size(x)

  n <- pmin(n, size)

  new <- vec_init(x, n)
  old <- vec_slice(x, -seq_len(n))

  vec_c(old, new)
}

cars <- mtcars[1:3,]

vec_lag(cars, 1)
#>   mpg cyl disp  hp drat    wt  qsec vs am gear carb
#> 1  NA  NA   NA  NA   NA    NA    NA NA NA   NA   NA
#> 2  21   6  160 110  3.9 2.620 16.46  0  1    4    4
#> 3  21   6  160 110  3.9 2.875 17.02  0  1    4    4

vec_lag(cars, 2)
#>   mpg cyl disp  hp drat   wt  qsec vs am gear carb
#> 1  NA  NA   NA  NA   NA   NA    NA NA NA   NA   NA
#> 2  NA  NA   NA  NA   NA   NA    NA NA NA   NA   NA
#> 3  21   6  160 110  3.9 2.62 16.46  0  1    4    4

vec_lag(cars, -1)
#> `n` must be positive.

vec_lead(cars, 1)
#>    mpg cyl disp  hp drat    wt  qsec vs am gear carb
#> 1 21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
#> 2 22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
#> 3   NA  NA   NA  NA   NA    NA    NA NA NA   NA   NA

vec_lead(cars, 2)
#>    mpg cyl disp hp drat   wt  qsec vs am gear carb
#> 1 22.8   4  108 93 3.85 2.32 18.61  1  1    4    1
#> 2   NA  NA   NA NA   NA   NA    NA NA NA   NA   NA
#> 3   NA  NA   NA NA   NA   NA    NA NA NA   NA   NA

^{Created on 2019-10-04 by the reprex package (v0.2.1)}

[hadley]

Moved to individual issues