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For the following data, how can i create a dictionary with id as the key and value of array of tuple [(x, y)]

  id  x  y
0  a  1  2
1  a  2  3
2  b  3  4

The expected dictionary is

{a: [(1,2), (2,3)], b:[(3,4)]}

user1901690
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  • Possibly a duplicate of http://stackoverflow.com/questions/26367812/appending-to-list-in-python-dictionary – Ray Toal Feb 01 '16 at 03:04

2 Answers2

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When iterating over the table (however you are doing it) check if the id is already in the dict and append to the existing value or add the new key:

data = {}
for id,x,y in SOURCE:
    if id in data:
        data[id].append((x,y))
    else:
        data[id] = [(x,y)]
Tadhg McDonald-Jensen
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1

The solution offered by @tadhg-mcdonald-jensen seems a perfect opportunity to take advantage of a defaultdict:

from collections import defaultdict

data = defaultdict(list)

with open(SOURCE_FILE_NAME) as source:
    for line in source:
        id, x, y = line.rstrip().split()
        data[id].append((x, y))

This avoids the decision to set or append -- simply append and let the defaultdict do the right thing for you.

cdlane
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