Using approx() with groups in dplyr

Question

I am trying to use approx() and dplyr to interpolate values in an existing array. My initial code looks like this ...

p = c(1,1,1,2,2,         


        

Answer 1

You can get the values you expect using dplyr.

library(dplyr)
Inputs %>%
  group_by(p) %>%
  arrange(p, q, .by_group = TRUE) %>%
  summarise(new.outputs = approx(x = q, y = r, xout = new.inputs)$y)

#     p  new.outputs
#  <dbl>       <dbl>
#     1         1.5
#     1         2.5
#     2         4.5
#     2         5.5

You can also get the values you expect using the ddply function from plyr.

library(plyr)

# Output as coordinates
ddply(Inputs, .(p), summarise, new.output = paste(approx(
  x = q, y = r, xout = new.inputs
)$y, collapse = ","))

# p new.output
# 1    1.5,2.5
# 2    4.5,5.5

#######################################

# Output as flattened per group p
ddply(Inputs,
      .(p),
      summarise,
      new.output = approx(x = q, y = r, xout = new.inputs)$y)

# p new.output
# 1        1.5
# 1        2.5
# 2        4.5
# 2        5.5