Write nested for loops in one sentence

Question

I have the following code:

list1 = [['a','b','c'],['d','e','f'],['g','h','i']]
sentences = []
for row in list1:
    for i in row:
        sentences.append(i)

print(sentences)

With the output:

['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']

How can I write that in one sentence? This is what I tried:

sentences = [i for i in row for row in list1]
print(sentences)

This is what I got:

['g', 'g', 'g', 'h', 'h', 'h', 'i', 'i', 'i']

You need to write it from left to right `[i for row in list1 for i in row]` — Moinuddin Quadri, Feb 03 '21 at 16:41

score 2 · Answer 1 · answered Feb 03 '21 at 16:39

2

Just need to give your list comprehension a switch in order.

sentences = [i for row in list1 for i in row ]
print(sentences)
['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']

answered Feb 03 '21 at 16:39

Correy Koshnick

That's awesome. You learn something every day! – Timo Vossen Feb 03 '21 at 16:41

score 2 · Accepted Answer · answered Feb 03 '21 at 16:39

2

You need to make the loop correct

[j for i in list1 for j in i]

['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']

Note: If the loop goes like

for b in a:
    for c in b:
        for d in c:
            ...

In list comprehension, it goes like

[... for b in a for c in b for d in c]

answered Feb 03 '21 at 16:39

Epsi95

kiranr · Answer 3 · 2021-02-03T16:54:29.883

2

x being the matrix

x = [['a','b','c'],['d','e','f'],['g','h','i']]

 [val 
     for sublist in x 
        for val in sublist]

The first line suggests what we want to append to the list. The second line is the outer loop and the third line is the inner loop.

edited Feb 03 '21 at 16:54

answered Feb 03 '21 at 16:40

kiranr

score 2 · Answer 4 · answered Feb 03 '21 at 16:41

2

list1 = [['a','b','c'],['d','e','f'],['g','h','i']]
a =[i for row in list1 for i in row]
print(a)

Just swap the order

answered Feb 03 '21 at 16:41

Prakash Dahal

4 Answers4