R – In R, what’s the simplest way to scale a vector to a unit vector

rscalingvector

In R, what's the simplest way to scale a vector to a unit vector?

For example, suppose

>vec
[1] 1 0 2 1

And

>vec / sqrt(sum(vec^2)) 
[1] 0.4082483 0.0000000 0.8164966 0.4082483

is its unit vector.

Is there some built-in function in R for this?

You could make yourself a function:

scalar1 <- function(x) {x / sqrt(sum(x^2))}

Now just use:

> scalar1(vec)
[1] 0.4082483 0.0000000 0.8164966 0.4082483

I use the tail function:

tail(vector, n=1)

The nice thing with tail is that it works on dataframes too, unlike the x[length(x)] idiom.

vector<T>::const_iterator first = myVec.begin() + 100000;
vector<T>::const_iterator last = myVec.begin() + 101000;
vector<T> newVec(first, last);

It's an O(N) operation to construct the new vector, but there isn't really a better way.