Need some suggestions in grouping of items

[MRAB]

On 2016-09-08 21:50, GP wrote:
>
> I have a list of items:
>     ShelvesToPack = [{'ShelfLength': 2278.0, 'ShelfWidth': 356.0, 'ShelfArea': 759152.0, 'ItemNames': 1},
>     {'ShelfLength': 1220.0, 'ShelfWidth': 610.0, 'ShelfArea':   372100.0, 'ItemNames': 2},
>     {'ShelfLength': 2310.0, 'ShelfWidth': 762.0, 'ShelfArea': 1760220.0, 'ItemNames': 3},
>     {'ShelfLength': 610.0, 'ShelfWidth': 610.0,   'ShelfArea': 1450435.0, 'ItemNames': 4}]
>
> I have a certain criteria and I  want to group the items based on those.
> I need the program that tells how many minimum number of groups one can have and how the items are grouped. I would like to form groups of these items such that (sum of shelflength (of itmes) <= max length or sum of  shelfwidth (of items) <= max width) and sum of ShelfArea (of items) <= Max Area. In this case, if we look at the logic we can have all the items packed in minimum 2 groups - item 1 and 3 will form one group and item 2 & 4 will form other group. I would like to have the answer in the format:
>     [[{'ShelfLength': 2278.0, 'ShelfWidth': 356.0, 'ShelfArea':    759152.0, 'ItemNames': 1} ,
>      {'ShelfLength': 2310.0, 'ShelfWidth':    762.0, 'ShelfArea': 1760220.0, 'ItemNames': 3}],
>     [{'ShelfLength':     1220.0, 'ShelfWidth': 610.0, 'ShelfArea':   372100.0, 'ItemNames': 2},
>      , {'ShelfLength': 610.0, 'ShelfWidth': 610.0,   'ShelfArea':   1450435.0, 'ItemNames': 4}]]
>
> I have written a code but it does only one grouping ( need some help why it doesnot for the remaining items and what corrections need to be done) .
>
> ShelvesToPack_sorted=sorted(ShelvesToPack, key = itemgetter('ShelfWidth'), reverse = True)
> AreaOfObject= 2972897.28
> current_width = 0
> current_length = 0
> current_area =0
> shelf =[]
> shelves=[]
> if len(ShelvesToPack_sorted) > 0:
>        for item in ShelvesToPack_sorted:
>             if (current_width + item['ShelfWidth'] <= 1219.2  or  current_length + item['ShelfLength']  <= 2438.5) and  current_area + item['ShelfArea'] <= AreaOfObject:
>                 shelf.append(item)
>                 current_width += item['ShelfWidth']
>                 current_length +=  item['ShelfLength']
>                 current_area += item['ShelfArea']
> del item
>
> if shelf:
>     shelves.append(shelf)
>
> print(shelves)
>
> This produces only one grouping and does not group the remaining items.
> [[{'ShelfLength': 2310.0, 'ItemNames': 3, 'ShelfArea': 1760220.0, 'ShelfWidth': 762.0}, {'ShelfLength': 2278.0, 'ItemNames': 1, 'ShelfArea': 759152.0, 'ShelfWidth': 356.0}]]
>
> Can anyone please suggest?
>
The easy way to do it is, in pseudocode:

shelves = []

while list_of_items:
     shelf = []
     # Also initialise width, length and area.
     doesnt_fit = []

     for item in list_of_items:
         if item fits:
             shelf.append(item)
             # Also adjust width, length and area.
         else:
             doesnt_fit.append(item)

     shelves.append(shelf)
     list_of_items = doesnt_fit