I would like to know how to do the summary of value contained in a matrix?I currently have this code for input of my matrix:
matrix = []
loop = True
while loop:
line = input()
if not line:
loop = False
values = line.split()
row = [int(value) for value in values]
matrix.append(row)
For example,the matrix [[1,2,3],[4,5,6]] would result 21,the summary of all the values.And im not quite sure on how to do that.
Thank you!
You can use the built-in sum() function. As your matrix isn't flat, but a list of lists, you need to flatten it for sum():
sum(val for row in matrix for val in row)
You can use list comprehension:
matrix = [[1, 2, 3], [4, 5, 6]]
sums = sum(y for x in matrix for y in x)
print sums
This runs as:
>>> matrix = [[1, 2, 3], [4, 5, 6]]
>>> sums = sum(y for x in matrix for y in x)
>>> print sums
21
>>>
Or you could use a basic for loop:
matrix = [[1, 2, 3], [4, 5, 6]]
sums = 0
for sub in matrix:
for value in sub:
sums+=value
print sums
This runs as:
>>> matrix = [[1, 2, 3], [4, 5, 6]]
>>> sums = 0
>>> for sub in matrix:
... for value in sub:
... sums+=value
...
>>> print sums
21
>>>
List comprehension is the same as the double for loops, only in one line:
Explanation of the following:
sums = sum(y for x in matrix for y in x)
Let's start at the beginning:
We use the builtin function sum() to calculate all the values in the list:
>>> sum([1, 2, 3, 4]) #Should be 10
10
>>>
However, sum() only works with flattened lists:
>>> sum([[1, 2], [3, 4]])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'int' and 'list'
>>>
Thus, we need to flatten it with double for loops:
sum(y for x in matrix for y in x)
The for x in matrix is basically taking every value of matrix, essentially [1, 2, 3] and [4, 5, 6] in this case. The for y in x is assigning y to every value of x, [1, 2, 3, 4, 5, 6]. This is our flattened out list. Then we call sum(), and everything works like magic!
here is a function that will do that
M = [[1,2,3],[4,5,6]]
def matrixSummary( M ):
rowSums=[]
for row in M:
rowSums.append( sum( row ))
return sum( rowSums )
matrixSummary( M )
// Result: 21 //
looks like CoDEmanX has a nice list comprehension version
