How do I find how many rows and columns are in a 2d array?
For example,
Input = ([[1, 2], [3, 4], [5, 6]])`
should be displayed as 3 rows and 2 columns.
asked May 23, 2012 at 3:19
Ronaldinho Learn Coding
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4sounds like you should be using a numpy array, not a list of listswim– wim2012-05-23 05:27:50 +00:00Commented May 23, 2012 at 5:27
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6 Answers
Like this:
numrows = len(input) # 3 rows in your example
numcols = len(input[0]) # 2 columns in your example
Assuming that all the sublists have the same length (that is, it's not a jagged array).
4 Comments
Makoto
So long as it's not a jagged array, this is ideal.
Ronaldinho Learn Coding
yo, I want to find sum of all element in that 2D array def sum1(input): sum = 0 for row in range (len(input)-1): for col in range(len(input[0])-1): sum = sum + input[row][col] return sum print sum1([[1, 2],[3, 4],[5, 6]]) It display 4 instead of 21 (1+2+3+4+5+6 = 21). Where is my mistake?
Óscar López
There's a simpler solution: sum(sum(x) for x in input)
Junuxx
@LongBodie: The mistake is that you subtract 1 from the lengths where you shouldn't.
Range(n) already gives 0,1,...,n-1 .You can use numpy.shape.
import numpy as np
x = np.array([[1, 2],[3, 4],[5, 6]])
Result:
>>> x
array([[1, 2],
[3, 4],
[5, 6]])
>>> np.shape(x)
(3, 2)
First value in the tuple is number rows = 3; second value in the tuple is number of columns = 2.
1 Comment
urgeo
Thank you, I didn't want to use numpy for this thing
In addition, correct way to count total item number would be:
sum(len(x) for x in input)
1 Comment
Bjarne Magnussen
Great, this was exactly what I needed! In my case I can count all elements of a list up to 2nd degree: sum(len(x) if isinstance(x, list) else 1 for x in some_list)
Assuming input[row][col],
rows = len(input)
cols = map(len, input) #list of column lengths
Comments
You can also use np.size(a,1), 1 here is the axis and this will give you the number of columns
Comments
assuming input[row][col]
rows = len(input)
cols = len(list(zip(*input)))
