Generating a dictionary with value zeroed and keys from list of lists

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#1

I was wondering about the idiomatic way Python to initialize a dictionary with all values set to zero and the keys coming from a list. A little research gave me the idea that dict.fromkeys was a common way and certainly seems pretty succinct.

colors = ['red', 'green', 'blue']
color_scores = dict.fromkeys(colors, 0)
# {'red': 0, 'green': 0, 'blue': 0}

I was also wondering about the idiomatic to obtain a list from a lists of lists i.e. given:

fruits = [['fruit_name', 'color', 'rating'], ['jonathan apple', 'red', 63], ['gala apple', 'green', 33], ['blueberry', 'blue', 99] ]

generate

['jonathan apple', 'gala apple', 'blueberry']

or combing the dictionary initialization, generate
{'jonathan apple': 0, 'gala apple': 0, 'blueberry': 0}

This following style sat well with popular approaches from other languages but I did not know if this was very idiomatic for Python, especially when used as nested expression

fruit_names = list(map( lambda row : row[0], fruits[1:]))
fruit_scores = dict.fromkeys(list(map( lambda row : row[0], fruits[1:])), 0)

The latter line would output what we were looking for:
{'jonathan apple': 0, 'gala apple': 0, 'blueberry': 0}

I had the impression that list comprehensions was a more idiomatic in Python for list transformation, and it looks pretty good for this example below

fruit_scores = dict.fromkeys([row[0] for row in fruits[1:]], 0)

Any feedback appreciated.

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#2

I think others might be able to help you better if you added a bit more detail on your actual input and expected output.

Lists don’t have columns. List of lists have rows, so you could consider them having columns too and I believe that’s what you might be referring to. But an example of the list of lists would be helpful.

And a sample of the expected output based on that list of lists would also be helpful.

Maybe then someone can try to suggest alternative ways to do this.

#3

Thanks for calling the poor wording on my question to attention as it did seem to be quite unclear when I reviewed it. I reworded this to focus on Python style for dictionary and list manipulation.

#4

Thanks for rewording it.

Since you are already aware of list comprehensions, I think the best possible way might be to use Dictionary Comprehension for this.

Something as simple as -

{val[0]:0 for val in fruits[1:]}

The above will yield the same result and for significantly large inputs, it is likely to be faster than your non-list comprehension approach.

Your list comprehension approach is comparable to the dictionary comprehension one. But the latter is more “pythonic” in this particular scenario.

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#5

Thanks, that’s what I was looking for

#6

I am just starting to learn the power of list comprehensions; they are so awesome! I never thought about dictionary comprehensions but it totally makes sense…I wonder where else we could apply such a “coding strategy?”

Also, @radlab773 would you kindly mark the_doctor’s answer above as being the solution, please & thank you!

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