CODEWITHSUNDEEP
rmathsum
gigibotte
gigibotte

Reputation: 11

How to compute summation of variables in r

I'm trying to compute a simple summation (to learn how these works on r and then use in a more complicate problem)in r.

This is the summation I'm trying to compute

!(https://i.sstatic.net/9ln8S.jpg)

sum_{i=1}^5 (x^i) where x is from 1:5.

basically the outcome should be either a vector composed like this (sum(1^i),sum(2^i),sum(3^i),sum(4^i),sum(5^i)) so that later I can sum it to get the overall sum or automatically the sum. (equal to 5699).

The code I've tried to use is the following:

for(i in 1:5){
  for(x in 1:5){
  a[i] <- sum(x^(i))
  }
  }
a

however the outcome is this vector 

[1]    5   25  125  625 3125

it's only doing the 1^5,2^5,3^5,4^5,5^5

Any idea of how to do it?

Upvotes: 0

Views: 1665

Answers (2)

pgigeruzh
pgigeruzh

Reputation: 191

It's certainly best to use built in functions (e.g. sapply, sum) in R because they are optimized and sometimes implemented in faster programming language such as C. For-loops on the other hand run inside R and can be very slow.

The following code should do what you asked for and may be helpful for learning purposes:

# initialize vector
a <- c()

for(x in 1:5) {
  # loop through all x

  # calculate sum for some x
  sum <- 0
  for(i in 1:5) {
    sum <- sum + x^i
  }
  # append result to vector a
  a <- c(a, sum)
}

print(a)
[1]    5   62  363 1364 3905
sum(a)
[1] 5699

Upvotes: 0

Julian_Hn
Julian_Hn

Reputation: 2141

This solves your problem without the need for a for-loop but the more R-like sapply

vec <- sapply(1:5,function(x) sum(x^(1:5)))

vec
[1]    5   62  363 1364 3905


Sum <- sum(vec)

Sum
[1] 5699

Upvotes: 1

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