Can I determine the index where two arrays cross?

Question

I have two arrays of values which represent the Y value. I am trying to determine if line1 and line2 crossover/under each other during the set and if possible, return the index in the array they do. I have found code that can tell me a specific line but trying to see if there a better way to do this?

The data sets are below. line1[0] would be the most recent number in the series. Below I would like to test if line2 crosses over line1 and this would return index 1.

line1 = [25, 30, 25, 20, 15, 10]
line2 = [ 60, 40, 20, 17, 11, 5]

So you are trying to find a common value between the two lists? — victor, Jun 23 '17 at 20:12
Possible duplicate of [Simplest code for array intersection in javascript](https://stackoverflow.com/questions/1885557/simplest-code-for-array-intersection-in-javascript) — Stephen R. Smith, Jun 23 '17 at 20:44
Are you trying to find the largest `i` such that `line1[i] <= line2[i]`? — David Knipe, Jun 23 '17 at 20:59

score 0 · Answer 1 · answered Jun 23 '17 at 20:35

0

var line1 = [25, 30, 25, 20, 15, 10];
var line2 = [ 60, 40, 20, 17, 11, 5];
var start=line1[0]<line2[0];
var crossingpoint=line1.findIndex((el,i)=>start!==(el<line2[i]));

Simply check if linepoint0 is bigger linepoint1 changes. In your case it will return 2, cause it crosses between 1 and 2. You may substract 1 to get the desired output...

try it

answered Jun 23 '17 at 20:35

Jonas Wilms

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This is correct if you do not consider equal values (i.e. positions where the arrays "touch") to be "crossing", which may or may not be the desired result. If you _do_ want to consider equal values to be "crossing" then add an equality test, i.e. add `el===line2[i]||` just before `start` in the final line. – Andrew Willems Jun 23 '17 at 23:27

Can I determine the index where two arrays cross?

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