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I have a 2D array in python modeled by a list of lists and I want to extract the column. I made a quick research and I found a way that uses numpy arrays. The problem is that I do not want to use numpy so I don't want to convert my list of lists into a numpy array and then use [:,1] syntax. I tried using it on a normal list of lists but it shows an error so it's not possible. I am asking for a similar thing for list of lists without having to go through each element(In numpy arrays, it's faster to access a column by using [:,1] syntax than iterating over the elements of the array).
I found this link but again it suggests iterating over elements without a shortcut.
Thanks in advance.
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Python provides an option of creating a list within a list. If put simply, it is a nested list but with one or more lists inside as an element. Here, [a,b], [c,d], and [e,f] are separate lists which are passed as elements to make a new list.
When you wish to print the list elements in a single line with the spaces in between, you can make use of the "*" operator for the same. Using this operator, you can print all the elements of the list in a new separate line with spaces in between every element using sep attribute such as sep=”/n” or sep=”,”.
List comprehensions are your friend when working with lists of lists:
In [111]: alist Out[111]: [[0, 1, 2, 3, 4, 5], [6, 7, 8, 9, 10, 11], [12, 13, 14, 15, 16, 17], [18, 19, 20, 21, 22, 23]] In [112]: [row[1] for row in alist] Out[112]: [1, 7, 13, 19] There's also a handy 'idiom' for transposing a nested list, turning 'columns' into 'rows':
In [113]: tlist = list(zip(*alist)) In [114]: tlist Out[114]: [(0, 6, 12, 18), (1, 7, 13, 19), (2, 8, 14, 20), (3, 9, 15, 21), (4, 10, 16, 22), (5, 11, 17, 23)] In [115]: tlist[1] Out[115]: (1, 7, 13, 19) If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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