How to add values ​between hours - r

Question

I have code that breaks down hours with corresponding values ​​into quarters of an hour.
Unfortunately, when broken down into quarters of an hour, the values ​​are identical for the entire hour.
After adding quarters of an hour, I would also like to add values ​​between the original hours so that the graph is smooth and not sharp. How to do it, average it, interpolate it?
df <- data.frame(
h = 0:23,
x = c(22, 11, 5, 8 , 22, 88, 77, 7, 11, 5, 8 , 22, 88, 77, 11, 5, 8 , 22, 88, 77, 11, 5, 8 , 22))
library(dplyr)
library(stringr)
df %>%
data.frame(h = rep(df$h, each = 4), # quadruplicate rows
x = rep(df$x, each = 4)) %>% # quadruplicate rows
mutate(h.1 = str_pad(h.1, width = 2, side = "left", pad = "0"), # add leading '0'
qu = paste0(h.1, c(":00", ":15", ":30", ":45"))) %>% # create quarters
select( - c(h,x)) %>% # deselect obsolete cols
rename(c("h" = "h.1", "x" = "x.1"))
df %>%
ggplot() +
geom_point(aes(qu, x), color = "red", size = 2) +
labs(x= "", y = "",
title = "Example")

Answer 1

Here I make a "decimal hour" variable to simplify the calculations. We can also use hms::hms() to define a timestamp that ggplot2 can understand. I use base:approx here to interpolate between hourly points.
df2 <- df %>%
tidyr::uncount(4) %>% # make 4 copies of each row
mutate(h_dec = h + (0:3)/4,
h_time = hms::hms(hours = h_dec),
x = x * c(1, NA, NA, NA), # this is to make non-hourly into NA,
# so that approx only uses hourly
x_interp = approx(x = h, y = x, xout=h_dec)$y)
df2 %>%
ggplot() +
geom_point(aes(h_time, x_interp), color = "red", size = 2) +
labs(x= "", y = "",
title = "Example")