I am a bit new to Python and I want to convert a 1D list to a 2D list, given the width and length of this matrix.
Say I have a list=[0,1,2,3] and I want to make a 2 by 2 matrix of this list.
How can I get matrix [[0,1],[2,3]] width=2, length=2 out of the list?
asked Feb 4, 2013 at 6:45
1
Try something like that:
In [53]: l = [0,1,2,3]
In [54]: def to_matrix[l, n]:
...: return [l[i:i+n] for i in xrange[0, len[l], n]]
In [55]: to_matrix[l,2]
Out[55]: [[0, 1], [2, 3]]
answered Feb 4, 2013 at 6:51
rootroot
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1
I think you should use numpy, which is purpose-built for working with matrices/arrays, rather than a list of lists. That would look like this:
>>> import numpy as np
>>> list_ = [0,1,2,3]
>>> a = np.array[list_].reshape[2,2]
>>> a
array[[[0, 1],
[2, 3]]]
>>> a.shape
[2, 2]
Avoid calling a variable list as it shadows the built-in name.
answered Feb 4, 2013 at 7:00
wimwim
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3
not as elegant and pretty specific to yours, but you create 2 lists [every other integer] and zip/list them back together.
full_list = [0, 1, 2, 3]
list1 = []
list2 = []
for i in full_list:
if i % 2 == 0:
list1.append[i]
else:
list2.append[i]
zip_list = zip[list1, list2]
done = list[zip_list]
output:
[[0, 1], [2, 3]]
answered Sep 8 at 4:20
Given a 2D list, Write a Python program to convert the given list into a flattened list.
Method #1: Using chain.iterable[]
Python3
from itertools import chain
ini_list = [[1, 2, 3],
[3, 6, 7],
[7, 5, 4]]
print ["initial list ", str[ini_list]]
flatten_list = list[chain.from_iterable[ini_list]]
print ["final_result", str[flatten_list]]
Output:
initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] final_result [1, 2, 3, 3, 6, 7, 7, 5, 4]
Method #2: Using list comprehension
Python3
from itertools import chain
ini_list = [[1, 2, 3],
[3, 6, 7],
[7, 5, 4]]
print ["initial list ", str[ini_list]]
flatten_list = [j for sub in ini_list for j in sub]
print ["final_result", str[flatten_list]]
Output:
initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] final_result [1, 2, 3, 3, 6, 7, 7, 5, 4]
Method #3: Using functools.reduce
Python3
from functools import
reduce
ini_list = [[1, 2, 3],
[3, 6, 7],
[7, 5, 4]]
print ["initial list ", str[ini_list]]
flatten_list = reduce[lambda z, y :z + y, ini_list]
print ["final_result", str[flatten_list]]
Output:
initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] final_result [1, 2, 3, 3, 6, 7, 7, 5, 4]
Method
#4: Using sum
sum has an optional argument: sum[iterable [, start]]
Python3
ini_list = [[1, 2, 3],
[3, 6, 7],
[7, 5, 4]]
print ["initial list ", str[ini_list]]
flatten_list = sum[ini_list, []]
print
["final_result", str[flatten_list]]
Output:
initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] final_result [1, 2, 3, 3, 6, 7, 7, 5, 4]
Method #5: Using lambda
Python3
ini_list=[[1, 2, 3],
[3, 6, 7],
[7, 5, 4]]
flatten_list =
lambda y:[x for a in y for x in flatten_list[a]] if type[y] is list else [y]
print["Initial list ",ini_list]
print["Flattened List ",flatten_list[ini_list]]
Output:
Initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] Flattened List [1, 2, 3, 3, 6, 7, 7, 5, 4]
Method #6: Using numpy
Python3
import numpy
ini_list=[[1, 2, 3],
[3, 6, 7],
[7 ,5, 4]]
print["Initial list ",ini_list]
print["Flattened List ",list[numpy.concatenate[ini_list].flat]]
Output:
Initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] Flattened List [1, 2, 3, 3, 6, 7, 7, 5, 4]
Method #7: Using extend[] method
Python3
ini_list=[[1, 2, 3],[3, 6, 7],[7
,5, 4]]
print["Initial list ",ini_list]
res=[]
for i in ini_list:
res.extend[i]
print["Flattened List ",res]
Output
Initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] Flattened List [1, 2, 3, 3, 6, 7, 7, 5, 4]