CODEWITHSUNDEEP
rfor-loop
Lord Nermal
Lord Nermal

Reputation: 1

Writing a for loop to add 1 to each element in a vector for R

Apologies for the dumb question, but I've just begun teaching myself programming and working with R and have been stuck on this question for a couple of days. I'm creating a vector that has three elements to it and then trying to write a for loop that adds one to each element. This is what I have so far.

```{r}
vec <- c(3, 1, 4) 
for (j in 1:dim(vec)[1]
vec = vec + 1
}

I tried looking at some examples and this was the closest I got, and I feel like it should work, but I keep getting errors. Any help would be greatly appreciated.

Upvotes: 0

Views: 9420

Answers (2)

rknuu
rknuu

Reputation: 329

R has vector aware functions. Most classic math operations are 'vectorized' .

The other trick is that some vectorized functions features recycling.

So when you do 

v <- c(1, 2, 4)
v <- v + 1

The number 1 is recycled as a vector that matches the size of v.

Given this, v+1 is the same as

v <- c(1, 2, 4) + c(1, 1, 1)

Note your for loop above has various syntax errors 

for (j in 1:dim(vec)[1] vec = vec + 1 }

Should be 

for (j in 1:length(vec)) { vec[j] <- vec[j] + 1}

Upvotes: 3

Kevin M
Kevin M

Reputation: 491

R is built around vectors, so functions and arithmetic can be performed on entire vectors. for loops will be much slower than making use of R's native vector-based operations. Just remove the for loop and it will work. As Pierre commented, only vec + 1 is needed.

vec <- c(3, 1, 4) 
vec <- vec + 1
print(vec)
#[1] 4 2 5

Though you would never do it this way, to fix your loop, do this:

vec <- c(3, 1, 4) 
for (j in 1:length(vec)){
    vec[j] = vec[j] + 1
}
print(vec)
#[1] 4 2 5

Upvotes: 1

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