Recursive function using dplyr

Question

I have data:

dat <- tibble(
         day = 200:210,
         x = sample(-10:10, size = 11,replace = T))

I have a variable y

Answer 1

df %>% mutate(y = 5 + cumsum(x))

or, with your extra conditions

df %>% mutate(y = (5 + cumsum(x)) %>% pmin(10) %>% pmax(0))

Answer 2

We could use accumulate from purrr. With accumulate, do the recursive sum of 'x' elements while initiating with a value of 5 (.init = 5) and remove the first element of accumulate output ([-1])

library(purrr)
library(dplyr)
dat %>%
     mutate(y = accumulate(x, ~ .x + .y, .init = 5)[-1])
# A tibble: 11 x 3
#     day     x      y
#   <int> <int>  <dbl>
# 1   200     4   9.00
# 2   201     3  12.0 
# 3   202    -4   8.00
# 4   203    -7   1.00
# 5   204    -3 - 2.00
# 6   205     1 - 1.00
# 7   206    -5 - 6.00
# 8   207    -1 - 7.00
# 9   208    -4 -11.0 
#10   209    -2 -13.0 
#11   210     4 - 9.00

---

A similar approach in base R would be

dat$y <- Reduce(function(u, v)  u + v , dat$x, init = 5, accumulate = TRUE)[-1]
dat$y
#[1]   9  12   8   1  -2  -1  -6  -7 -11 -13  -9