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pythonsortingnested-lists

Sort nested lists by list

How can I efficiently sort nested lists by the first element of each nested list matching the order given in order list?

List of lists: [[97, 2, 0, 2], [97, 2, 0, 2], [98, 1, 2, 3], [99, 3, 3, 6], [99, 3, 3, 6], [99, 3, 3, 6], [101, 1, 6, 7], [100, 1, 7, 8]]

Order list: [97, 98, 99, 99, 101, 100, 97, 99]

Desired list: [[97, 2, 0, 2], [98, 1, 2, 3], [99, 3, 3, 6], [99, 3, 3, 6], [101, 1, 6, 7], [100, 1, 7, 8], [97, 2, 0, 2], [99, 3, 3, 6]]

Solution

  • Try creating a dict keyed to the first value from your nested list. Then build the output list from that dict:

    nl = [[97, 2, 0, 2], [97, 2, 0, 2], [98, 1, 2, 3], [99, 3, 3, 6], [99, 3, 3, 6],
      [99, 3, 3, 6], [101, 1, 6, 7], [100, 1, 7, 8]]

# Associate first value in list to the list
d = {v[0]: v for v in nl}

order_lst = [97, 98, 99, 99, 101, 100, 97, 99]

# Grab the list associated to each value in order_list from d
out = [d[v] for v in order_lst]
print(out)

    out:

    [[97, 2, 0, 2], [98, 1, 2, 3], [99, 3, 3, 6], [99, 3, 3, 6], [101, 1, 6, 7], 
[100, 1, 7, 8], [97, 2, 0, 2], [99, 3, 3, 6]]

    *Note this assumes that all sub-lists in the nested list are acceptable values as multiple variants of the same key are not supported in a dict.