Calculation within a pipe between different rows of a data frame - r

Question

I have a tibble with a column of different numbers. I wish to calculate for every one of them how many others before them are within a certain range.
For example, let's say that range is 200 ; in the tibble below the result for the 5th number would be 2, that is the cardinality of the list {816, 705} whose numbers are above 872-1-200 = 671 but below 872.
I have thought of something along the lines of :
for every theRow of the tibble, do calculate the vector theTibble$number_list between(X,Y) ;
summing the boolean returned vector.
I have been told that using loops is less efficient.
Is there a clean way to do this within a pipe without using loops?

Answer 1

Not the way you asked for it, but you can use a bit of linear algebra. Should be more efficient and more simple than a loop.
number_list <- c(248,650,705,816,872,991,1156,1157,1180,1277)
m <- matrix(number_list, nrow = length(number_list), ncol = length(number_list))
d <- (t(m) - number_list)
cutoff <- 200
# I used setNames to name the result, but you do not need to
# We count inclusive of 0 in case of ties
setNames(colSums(d >= 0 & d < cutoff) - 1, number_list)
Which gives you the following named vector.
248 650 705 816 872 991 1156 1157 1180 1277
0 0 1 2 2 2 1 2 3 3
Here is another way that is pipe-able using rollapply().
library(zoo)
cutoff <- 200
df %>%
mutate(count = rollapply(number_list,
width = seq_along(number_list),
function(x) sum((tail(x, 1) - head(x, -1)) <= cutoff),
align = "right"))
Which gives you another column.
# A tibble: 10 x 2
number_list count
<int> <int>
1 248 0
2 650 0
3 705 1
4 816 2
5 872 2
6 991 2
7 1156 1
8 1157 2
9 1180 3
10 1277 3