CODEWITHSUNDEEP
pythonlistdictionary
letsc
letsc

Reputation: 2567

Python - Split List into a Dictionary

I am trying to split a big list into a dictionary. Given a list with say 363 elements I want to divide them such that each key in the dictionary will have a list of 10 values. So a list of 363 elements will have 37 keys (rounded up to nearest 10).The keys will start from 1 and go upto 37. I wrote a function for the rounding up but i dont know how to split the list while making sure the sequence is maintained and if all the lists (which will be the values of the keys) are joined they will mirror the original list.

This is my rounding up function:

def roundup(list_length, atatime=10):
    return ((atatime-(list_length%atatime))+list_length)/atatime

Any ideas , suggestions will be really helpfull

Upvotes: 1

Views: 1644

Answers (2)

Padraic Cunningham
Padraic Cunningham

Reputation: 180550

If you want to round up and slice appropriately:

l = list(range(363)) 
at_a_time = 10
n = len(l)
d, r = divmod(n, at_a_time) 

# if there is a remainder, add 1 to the keys, 363 -> 37 keys 360 -> 36 keys
num_keys = d + 1 if r else d
# get correct slice size based on amount of keys    
sli = n // num_keys

# create "sli" sized chunks
vals = (l[i:i+sli] for i in range(0, n, sli+1)) 
# make dict from `1 to num_keys inclusive and slices
dct = dict(zip(range(1,num_keys+1),vals))
print(dct)
{1: [0, 1, 2, 3, 4, 5, 6, 7, 8], 2: [10, 11, 12, 13, 14, 15, 16, 17, 18], 3: [20, 21, 22, 23, 24, 25, 26, 27, 28], 4: [30, 31, 32, 33, 34, 35, 36, 37, 38], 5: [40, 41, 42, 43, 44, 45, 46, 47, 48], 6: [50, 51, 52, 53, 54, 55, 56, 57, 58], 7: [60, 61, 62, 63, 64, 65, 66, 67, 68], 8: [70, 71, 72, 73, 74, 75, 76, 77, 78], 9: [80, 81, 82, 83, 84, 85, 86, 87, 88], 10: [90, 91, 92, 93, 94, 95, 96, 97, 98], 11: [100, 101, 102, 103, 104, 105, 106, 107, 108], 12: [110, 111, 112, 113, 114, 115, 116, 117, 118], 13: [120, 121, 122, 123, 124, 125, 126, 127, 128], 14: [130, 131, 132, 133, 134, 135, 136, 137, 138], 15: [140, 141, 142, 143, 144, 145, 146, 147, 148], 16: [150, 151, 152, 153, 154, 155, 156, 157, 158], 17: [160, 161, 162, 163, 164, 165, 166, 167, 168], 18: [170, 171, 172, 173, 174, 175, 176, 177, 178], 19: [180, 181, 182, 183, 184, 185, 186, 187, 188], 20: [190, 191, 192, 193, 194, 195, 196, 197, 198], 21: [200, 201, 202, 203, 204, 205, 206, 207, 208], 22: [210, 211, 212, 213, 214, 215, 216, 217, 218], 23: [220, 221, 222, 223, 224, 225, 226, 227, 228], 24: [230, 231, 232, 233, 234, 235, 236, 237, 238], 25: [240, 241, 242, 243, 244, 245, 246, 247, 248], 26: [250, 251, 252, 253, 254, 255, 256, 257, 258], 27: [260, 261, 262, 263, 264, 265, 266, 267, 268], 28: [270, 271, 272, 273, 274, 275, 276, 277, 278], 29: [280, 281, 282, 283, 284, 285, 286, 287, 288], 30: [290, 291, 292, 293, 294, 295, 296, 297, 298], 31: [300, 301, 302, 303, 304, 305, 306, 307, 308], 32: [310, 311, 312, 313, 314, 315, 316, 317, 318], 33: [320, 321, 322, 323, 324, 325, 326, 327, 328], 34: [330, 331, 332, 333, 334, 335, 336, 337, 338], 35: [340, 341, 342, 343, 344, 345, 346, 347, 348], 36: [350, 351, 352, 353, 354, 355, 356, 357, 358], 37: [360, 361, 362]}

If you don't want the list sliced evenly and the remainder to be added to the last key just use your atatime for each slice (10 in the example code):

 vals = (l[i:i+at_a_time] for i in range(0, n, sli+1))

We can also use num_keys = n + (at_a_time - 1) // at_a_time to round as any value that has a remainder // at_a_time will be rounded up adding at_a_time - 1 to it , any number evenly divisible will not.

You can do it all in a dict comprehension making some changes to the code but I think you will hopefully learn more from explicit code.

Upvotes: 1

sheba
sheba

Reputation: 850

The following dict comprehension slices the list into the required number of slices.

In other words, idx+1 is the key, whereas lst[atatime*idx:atatime*(idx+1)] is the value of a dictionary defined using dict-comprehension. The value is a slice of atatime length. We iterate over the (rounded upwards) size of the list divided by the chunk-size using an xrange iterator.

from math import ceil
{idx+1: lst[atatime*idx:atatime*(idx+1)] for idx in xrange(int(ceil(float(len(lst))/atatime)))}

Upvotes: 0

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