Question

I’m creating a display interface of lets say ‘products’. For this example lets say the display will show at max 4 products. There are a variable number of sources that the products can came from. The number of sources will never be larger than the number of products to display (at most 4 sources for this example). Each source contains 1 or more products. The goal is to evenly distribute the number of products displayed across the sources.

The logic for 4 products would be handled as follows.

• If there is 1 source, then 4 items will be selected from that source.
  (4×1)
• If there are 4 sources, then 1 item will be selected from each
  source. (1×1+1×1+1×1+1×1)
• If there are 2 sources, then 2 items will be selected from each
  source (2×1+2×1), unless one source only has 1 product, then it will follow as (1×1+3×1)
• If there are 3 sources, then 1 item will be selected from 2
  sources and 2 items will be selected from 1 source (2×1+1×1+1×1)

Before I start looping to output products, I have a collection of sources and the count of items in each source.

My question is:

What is the simplest way to loop through each source and output the
appropriate amount of products?

Keep in mind that each source may only have 1 product, so it is possible that 4 products cannot be selected.

Answer 1

Here is simple Python code to select the products.

It works by looping over the sources and adding one product at a time.

This should result in a fair distribution between the sources.

The code could be made much more efficient if you find it is too slow.

Z=[1,10,10]       # Number of products available for each source
Y=len(Z)          # Number of sources
X=4               # number of products to output
B=[0]*Y           # Number of products to select for each source

a=0               # Next source to try and take a product from
while sum(B)<min(sum(Z),X):
    a=(a+1)%Y     # Change to a different source for the next product
    if B[a]<Z[a]: # Check that this source still has products left
        B[a]+=1   # Note that we have taken a product from source a

print B

In this example it prints

[1, 2, 1]

to signify taking 1 product from the first source, 2 from the second, and 1 from the third.