Map an array into another array

Question

I have an array of dict like:

[{'id': 1, 'tags': ['tag_a', 'tag_b']}, {'id': 2, 'tags': ['tag_c', 'tag_b']}]

and I would like to convert this array into a new array based on ticket_id and each tag value should be an object in the array.

I almost did it using the following function:

raw = [{'id': 1, 'tags': ['tag_a', 'tag_b']}, {'id': 2, 'tags': ['tag_c', 'tag_b']}]

def transform(ticket):
    result = []
    for tag in ticket.get('tags', []):
        result.append({'ticket_id': ticket.get('id'), 'tag': tag, 'sync': '123'})
    return result

print(list(map(transform, raw)))

But it's returning something like [[{...}], [{...}]] and the syntax looks strange.

What is the right approach to return something like:

[{'ticket_id': 1, 'tag': 'tag_a', 'sync': '123'}, {'ticket_id': 1, 'tag': 'tag_b', 'sync': '123'}, ...]

juanpa.arrivillaga · Accepted Answer · 2019-05-30 22:48:34Z

3

You just need to flatten your results. Essentially, you used a map operation when you wanted a flat-map operation.

You can do this in one go by using a nested list comprehension:

[x for ticket in raw for x in transform(ticket)]

Of course, you could have done something like:

[x for xs in map(transform, raw) for x in xs]

Or just a regular nested loop would work.

answered May 30, 2019 at 22:48

juanpa.arrivillaga

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Sheldore · Accepted Answer · 2019-05-30 22:52:07Z

2

This is one way to do it using nested for loops. Moreover, you don't need to map your function. You can just pass the list to the function and print. The problem with your code was that you were using a single for loop whereas, the depth (length) of your tags was more than one

raw = [{'id': 1, 'tags': ['tag_a', 'tag_b']}, {'id': 2, 'tags': ['tag_c', 'tag_b']}]

def transform(ticket):
    result = []
    for dic in raw:
        for tag in dic['tags']:
            result.append({'ticket_id': dic['id'], 'tag': tag, 'sync': '123'})
    return result

print(transform(raw))
# [{'ticket_id': 1, 'tag': 'tag_a', 'sync': '123'}, {'ticket_id': 1, 'tag': 'tag_b', 'sync': '123'}, 
#  {'ticket_id': 2, 'tag': 'tag_c', 'sync': '123'}, {'ticket_id': 2, 'tag': 'tag_b', 'sync': '123'}]

edited May 30, 2019 at 22:52

answered May 30, 2019 at 22:49

Sheldore

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