python list comprehension: making list of multiple items from each list within a list of lists

Question

I have a list of lists, each with four items. For each list within it, I want to take indexes 0 and 2, put them in a list, then put all those lists in one list of lists. So, using for loops, I got what I wanted by doing this:

finallist = []
for i in range(len(weather_data)):
    templist = []
    templist.append(weather_data[i][0])
    templist.append(weather_data[i][2])
    finallist.append(templist)

so that gets me a list like [['2018-02-01', -18.6], ['2018-02-02', -19.6], ['2018-02-03', -22.3]]. But for this assignment, I'm supposed to do that by using one list comprehension. Best I can get is this:

 weekendtemps = [x[0] for x in weather_data if (x[1] == "Saturday" or x[1] == "Sunday")]

But that only gives me [['2018-02-01'], ['2018-02-2'], ['2018-02-03']]. How do I get both weather_data[0] and weather_data[2] using list comprehension?

You can have an empty list literal like the ones you’re using, [], but you can also have list literals with items inside. [1, 2, 3] — Ry-
– Ry- ♦, Commented Feb 7, 2019 at 4:57
Just add x[2] to what you tried in your one list comprehension — bumblebee
– bumblebee, Commented Feb 7, 2019 at 4:59

U13-Forward · Accepted Answer · 2019-02-07 04:57:46Z

2

Why not:

weekendtemps = [[x[0],x[2]] for x in weather_data if (x[1] == "Saturday" or x[1] == "Sunday")]

Or more efficient:

weekendtemps = [[x[0],x[2]] for x in weather_data if x[1] in ['Saturday', 'Sunday']]

answered Feb 7, 2019 at 4:57

U13-Forward

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