CODEWITHSUNDEEP
rloopsnestedrstudio
Bailey
Bailey

Reputation: 15

How do I make a nested for loop in R that multiples X & X?

So I'm trying to do a nested for loop that will multiple 1:100 with 1:100 (10,000 possible combinations). So 1*1, 1*2 ... 1* 100. Once it reaches 100, I want it to repeat, so 2*1, 2*2, 2*100.

Of note: I need to be doing this using for loops

table<-matrix(ncol=3, nrow=100*100)
for (i in 1:100) {
  for (z in 1:100){
    answer<-i*z
    table[i,] <- c(i,z,answer)
  }
}

Here's my code above. It seems like an easy fix, but I'm missing something..

Upvotes: 1

Views: 41

Answers (1)

akrun
akrun

Reputation: 887961

We can use outer

out <- outer(1:100, 1:100)

It can be converted to a 3-column data.frame with melt

library(reshape2)
out2 <- melt(out)

In the for loop, we need

for (i in 1:100) {
   for (z in 1:100){
       answer<-i*z
       table[i, z] <- answer
   }
  }
  table[i, z] <- answer

where

table <- matrix(nrow = 100, ncol = 100)

Checking the output

all.equal(out, table)
#[1] TRUE

If we need the 'i', 'z'

out2 <- transform(expand.grid(i = 1:100, z = 1:100), answer = i * z)

Or with crossing

library(tidyr)
library(dplyr)
crossing(i = 1:100, z = 1:100) %>%
   mutate(answer = i * z)
# A tibble: 10,000 x 3
#       i     z answer
#   <int> <int> <int>
# 1     1     1     1
# 2     1     2     2
# 3     1     3     3
# 4     1     4     4
# 5     1     5     5
# 6     1     6     6
# 7     1     7     7
# 8     1     8     8
# 9     1     9     9
#10     1    10    10
# … with 9,990 more rows

Or in a forloop

table1 <- c()
for(i in 1:100) {
   for(z in 1:100){
      table1 <- rbind(table1, c(i, z, i * z))
    }
 }

Upvotes: 1

Related Questions