bcdata_selection_Untitled-1

library(tidyverse)

first_year <- tibble(year = 2010, z = 1, x = 2, y = 3)

all_years <- first_year %>%
    bind_rows(tibble(year = 2011:2015))

all_years %>%
    summarise(
        year = year,
        accumulate(
            .init = tibble(
                x = first(all_years$x),
                y = first(all_years$y),
                z = first(all_years$z)
            ),
            .x = seq(length(z) - 1), # because we're supplying 1 row in init - tripped me up
            .f = function(inputs, x_ignored) {
                tibble(
                    z = 0.5 * inputs$x,
                    x = 0.5 * z + 0.5 * inputs$y,
                    y = 0.25 * inputs$x
                )
            }
        ) %>%
        bind_rows()
    )