# [R] Converting from Continuous 2D Points to Continuous 2D Vectors

Boris Steipe boris.steipe at utoronto.ca
Fri Dec 18 03:59:57 CET 2015

```Ok. And what is the problem now?

B.

On Dec 17, 2015, at 4:25 PM, Sidoti, Salvatore A. <sidoti.23 at buckeyemail.osu.edu> wrote:

> Greetings!
>
> I have a fairly large dataframe (df) with pathing information in the form of continuous x,y coordinates:
>
> df\$x
> df\$y
>
> With these data, I would like to:
> 1. Calculate a set of continuous vectors
> 2. Determine the angle between each of these vectors (in degrees)
> 3. Count the number of angles in the dataframe that meet a certain threshold (i.e. <90°)
>
> Here's what I've come up with so far:
>
> ### Function that calculates the angle between two vectors in 2D space:
>
> angle <- function(x,y){ # x and y are vectors
>  dot.prod <- x%*%y
>  norm.x <- norm(x,type="2")
>  norm.y <- norm(y,type="2")
>  theta <- acos(dot.prod / (norm.x * norm.y))
>  (180*as.numeric(theta))/pi # returns the angle in degrees
> }
>
> ### Test the function:
> x <- as.matrix(c(2,1))
> y <- as.matrix(c(1,2))
> angle(t(x),y)
>  36.8699
>
> Thank you!
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