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I have two arrays :

array_x = [x1, x2, x3, x4... xn]
array_y = [y1, y2, y3, y4... yn]

I would like to have a function f(array_x, array_y, value_x) that returns the value_y associated to the value_x by interpolation into the arrays.

How to do that ?

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    It is not entirely clear what you are looking for. Do you want the value from array_y that is in the position corresponding to where value_x is in array_x? Commented Mar 5, 2013 at 13:27
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    @Noio: Say you have values [1,2,3] at times [10,20,30], the idea is to iterpolate the value at say time 24. There are lots of ways to do this. The simplest is just a piecewise linear interpolation, which is what numpy.interp uses. Commented Mar 5, 2013 at 13:35

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I think that numpy.interp is exactly what you want. e.g.:

numpy.interp(value_x,array_x,array_y)

Note that here value_x can be a scalar or another array-like value. If it is an array-like value, you will be returned an array of corresponding interpolated values.

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3 Comments

Hm... How to write this my own? Some people complain that they got no numpy, so I need this myself...
Linear interpolation is a pretty well known algorithm. From there, it's just a matter of searching the array (could use bisection) for the elements that bound the value where you want to interpolate to -- With that said, for any real mathematical analysis, numpy seems to be the standard. Is there a reason why those people can't install numpy?
When I make game, I wouldn't want to place a tester for numpy(if it is installed) and installer(if it is not). So...

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