Splitting a list into N parts of approximately equal length

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迷失自我
迷失自我 2020-11-22 16:16

What is the best way to divide a list into roughly equal parts? For example, if the list has 7 elements and is split it into 2 parts, we want to get 3 elements in o

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  • 2020-11-22 16:59

    If you divide n elements into roughly k chunks you can make n % k chunks 1 element bigger than the other chunks to distribute the extra elements.

    The following code will give you the length for the chunks:

    [(n // k) + (1 if i < (n % k) else 0) for i in range(k)]
    

    Example: n=11, k=3 results in [4, 4, 3]

    You can then easily calculate the start indizes for the chunks:

    [i * (n // k) + min(i, n % k) for i in range(k)]
    

    Example: n=11, k=3 results in [0, 4, 8]

    Using the i+1th chunk as the boundary we get that the ith chunk of list l with len n is

    l[i * (n // k) + min(i, n % k):(i+1) * (n // k) + min(i+1, n % k)]
    

    As a final step create a list from all the chunks using list comprehension:

    [l[i * (n // k) + min(i, n % k):(i+1) * (n // k) + min(i+1, n % k)] for i in range(k)]
    

    Example: n=11, k=3, l=range(n) results in [range(0, 4), range(4, 8), range(8, 11)]

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  • 2020-11-22 16:59

    I tried most part of solutions, but they didn't work for my case, so I make a new function that work for most of cases and for any type of array:

    import math
    
    def chunkIt(seq, num):
        seqLen = len(seq)
        total_chunks = math.ceil(seqLen / num)
        items_per_chunk = num
        out = []
        last = 0
    
        while last < seqLen:
            out.append(seq[last:(last + items_per_chunk)])
            last += items_per_chunk
    
        return out
    
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  • 2020-11-22 17:00
    #!/usr/bin/python
    
    
    first_names = ['Steve', 'Jane', 'Sara', 'Mary','Jack','Bob', 'Bily', 'Boni', 'Chris','Sori', 'Will', 'Won','Li']
    
    def chunks(l, n):
    for i in range(0, len(l), n):
        # Create an index range for l of n items:
        yield l[i:i+n]
    
    result = list(chunks(first_names, 5))
    print result
    

    Picked from this link, and this was what helped me. I had a pre-defined list.

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  • 2020-11-22 17:01

    You can write it fairly simply as a list generator:

    def split(a, n):
        k, m = divmod(len(a), n)
        return (a[i * k + min(i, m):(i + 1) * k + min(i + 1, m)] for i in range(n))
    

    Example:

    >>> list(split(range(11), 3))
    [[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10]]
    
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  • 2020-11-22 17:02

    Using list comprehension:

    def divide_list_to_chunks(list_, n):
        return [list_[start::n] for start in range(n)]
    
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  • 2020-11-22 17:02
    def chunk_array(array : List, n: int) -> List[List]:
        chunk_size = len(array) // n 
        chunks = []
        i = 0
        while i < len(array):
            # if less than chunk_size left add the remainder to last element
            if len(array) - (i + chunk_size + 1) < 0:
                chunks[-1].append(*array[i:i + chunk_size])
                break
            else:
                chunks.append(array[i:i + chunk_size])
                i += chunk_size
        return chunks
    

    here's my version (inspired from Max's)

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