1

I am trying to index a numpy array with custom index. I understand that index can only be integers.

Some of the two number pair that I have looks like: 

400, 200
300, 100
500, 60

I want to generate unique integers from this pair so that I could use them to index a numpy array. Like, 

npArray[400200, 1] = someVal
npArray[300100, 2] = someOtherVal

The problem is, the size of my numpy array is only 4000 * 2. How can I generate unique identifiers from those pairs that falls into this 4000 range?

Thanks in advance.

QuestionEverything
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  • I don't think SO is the correct place for this kind of question. As you are looking for a one-to-one function this is a math problem, not a programming one. – DeepSpace Dec 28 '16 at 09:19
  • What are the limits of the two columns - Col0 min, max and similarly for Col1? – Divakar Dec 28 '16 at 09:20

2 Answers2

5

As far as I understand your question, you are looking for a way to create a function one-to-one in order to generate one integer using two other ones. Look at the picture below, this is a function that implements it:

enter image description here

Speaking about Python implementation, here's my code for it (for Python 3.x):

def pack(i1, i2):
    if i1 > i2:
        return i1**2 + i2
    else:
        return (i2 + 1)**2 - 1 - i1


def unpack(i):
    mx = int(i**0.5)
    s = (mx**2 + (mx + 1)**2 - 1) // 2
    if s >= i:
        return mx, mx - s + i
    else:
        return mx - i + s, mx


i = pack(3, 5)
print(i) # 32

i1, i2, = unpack(i)
print(i1, i2) # 3 5

print(pack(400, 200)) # 160200
print(unpack(160200)) # (400, 200)

print(pack(300, 100)) # 90100
print(unpack(90100)) # (300, 100)

print(pack(500, 60)) # 250060
print(unpack(250060)) # (500, 60)

This index in unique because I always am able to calculate initial two integers.

Fomalhaut
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0

You could create an intermediate index and use that index value for numpy array:

List1 = [400,300,500,400]
List2= [200,100,60,200]

zipList = list(set(zip(List1,List2)))

def getIndex(Val1,Val2):
    a = zipList.index((Val1,Val2))
    return a

print getIndex(400,200)

Answer: 2

This 2 can now be used to index the array. zipList[2] will return (400,200). The values will be integers and always be unique.

Oxymoron88
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