CODEWITHSUNDEEP
rdplyr
Faustin Gashakamba
Faustin Gashakamba

Reputation: 171

How to generate a random integers vector that sums up to a given number in R

I have a dataframe my_df and I would like to add an additional column, my_new_column, and populate it with random integer numbers that add up to a given sum. Here is some reproducible code:

library(dplyr)
library(magrittr)
my_df <- as.data.frame(matrix(nrow = 10, ncol = 2))
colnames(my_df) <- c("Cat", "MarksA")
my_df$Cat <- LETTERS[1:nrow(my_df)]
my_df$MarksA <- sample(1:100, size = nrow(my_df))

In Tidyverse style, I tried the following:

my_df %<>% mutate(my_new_column=sample(n()))

However, this gives me a column which sums up to an arbitrary number. How can I tweak my code to achieve this task?

Upvotes: 2

Views: 719

Answers (2)

Julien
Julien

Reputation: 1695

Since the sum of all numbers between 1 and n is equal to n(n + 1)/2, you may try something like this :

nb <- nrow(my_df)
my_df %<>% mutate(my_new_column = sample(nb * (nb + 1)/2))

Upvotes: 0

Harrison Jones
Harrison Jones

Reputation: 2506

Since you didn't specify a specific distribution, would this work? I pulled my answer mostly from this post which has more details and more options: Generate non-negative (or positive) random integers that sum to a fixed value

my_df %>%
  mutate(int_sample = rmultinom(n = 1, size = 1000, prob = rep.int(1 / 10, 10)))

Upvotes: 3

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