Is there a fast way to compare one element in a numpy array to the rest of the elements in that array?

arrays, numpy, python

Solution

The first value that is greater than a later value necessarily corresponds to the minimum among local minima:

k = np.array([0,1,2,3,4,5,6,5,4,10])
lm_i = np.where(np.diff(np.sign(np.diff(k))) > 0)[0] + 1
mlm = np.min(k[lm_i])
mlm_i = lm_i[np.argmin(k[lm_i])]

The index of the first value greater than a later value is then the first index greater than that minimum local minimum:

i = np.where(k > mlm)[0][0]

(Ignore that the graph appears to cross the horizontal line at the tangent; that's just a display artefact.)

As a one-liner:

np.where(k > np.min(k[np.where(np.diff(np.sign(np.diff(k))) > 0)[0] + 1]))[0][0]

Note that this is approx. 1000 times faster than root's solutions, as it is entirely vectorised:

%timeit np.where(k > np.min(k[np.where(np.diff(np.sign(np.diff(k))) > 0)[0] + 1]))[0][0]
1000 loops, best of 3: 228 us per loop

Problem

I have an array, and I want to see if any element in that array is greater than or equal to any other element in that array. I could do two for loops, but my array has a length of 10,000 or greater, and so that created a very slow program. Anyway I can do this faster? [EDIT] I only need it to see if it's greater than or equal to the elements that come after the element I am looking at, and if it is, I need to know it's index. [EDIT] I am going to re-explain my problem more clearly, because the current solutions aren't working for what I am needing. To start off, here is some code ``` x=linspace(-10, 10, 10000) t=linspace(0,5,10000) u=np.exp(-x**2) k=u*t+x ``` So I take an x array, get the height of that by putting it into the Gaussian, then based on that height, that is the speed at which that x value is propagating through space, which I find with k. My problem is, I need to find when the Gaussian becomes a double-valued function (or in other words, when a shock happens). If I do argmax solution, I will always get the last value in k because it is very close to zero, I need the first value after the element that will give me a double value in my function. [Edit] Small Example ``` x=[0,1,2,3,4,5,6,7,8,9,10] #Input k=[0,1,2,3,4,5,6,5,4,10] #adjusted for speed output I want in this case, 5 is the first number that goes above a number that comes after it. So I need to know the index of where 5 is located and possibly the index of the number that it is greater than ```

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