How to get each row in Python?

Question

I need to do this:

"""
Program a function

    def increasing (m)

that will be able, for any matrix m of positive integers, to check whether the sums of the rows in this array are increasing.

examples
1 3 2 5        The sums of the rows        2 8 4 1        The sums of the rows
7 9 4 1        are 11, 21 and 23.          6 2 8 5        are 15, 21 and 15.
3 5 6 9        --> increasing              8 4 2 1        --> not increasing
"""

So, I want to use sum(), which is perfectly doable, I guess.

I started like this:

def increasing (m):
    for row in m:
        row[1]

But I know that row[1] will just output the numbers in index 1 of each row. What I have in my mind is this:

def increasing (m):
    for row in m:
        if sum(row)[first_row] > sum(row)[second_row]:
           return False

But that is just slicing it, so I don't know how to count the rows so that I can compare them.

I don't want to use any module or whatsoever, just plain simple Python. Can someone point me in the right direction? I just need it to be as simple as possible.

Input format sample:

increasing_l = [
    [1, 3, 2, 5],
    [7, 9, 4, 1],
    [3, 5, 6, 9]
]

not_increasing_l = [
    [2, 8, 4, 1],
    [6, 2, 8, 5],
    [8, 4, 2, 1]
]

test1 = increasing(increasing_l)
test2 = increasing(not_increasing_l)

print "should be True: %s" % test1
print "should be False: %s" % test2

what is your input format like?

Danii-Sh
– Danii-Sh

2017-12-16 15:26:15 +00:00
Commented Dec 16, 2017 at 15:26 — Danii-Sh
– Danii-Sh, Commented Dec 16, 2017 at 15:26
Added that @HamedTemsah

Siyah
– Siyah

2017-12-16 15:27:14 +00:00
Commented Dec 16, 2017 at 15:27 — Siyah
– Siyah, Commented Dec 16, 2017 at 15:27

user2390182 · Accepted Answer · 2017-12-21 17:00:25Z

10

You can do the following:

def increasing(m):
    return all(sum(r1) < sum(r2) for r1, r2 in zip(m, m[1:]))

This uses zip to pair adjacent rows and all to efficiently do the pairwise sum comparison.

Without zip:

return all(sum(m[i-1]) < sum(m[i]) for i in range(1, len(m)))

edited Dec 21, 2017 at 17:00

answered Dec 16, 2017 at 15:28

user2390182

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4 Comments

Siyah Over a year ago

Hi, thank you. What if I wouldn't want to use zip? What is the alternative?

Joe Iddon Over a year ago

This does do more sums than necessary

user2390182 Over a year ago

@JoeIddon True, but I'll keep it or it will lose some of its conciseness and intuitive readability.

Joe Iddon Over a year ago

@schwobaseggl Yeah, it's definitely a very clever answer as it stands :)

oBit91 · Accepted Answer · 2017-12-16 15:30:57Z

7

Assuming that you have a function "sum" which returns the sum of given row. You can use a temp variable to keep the sum of your current row and use it for verification. For exmaple:

def increasing (m):
    prevRow = 0
    currentRow = 0
    for row in m:
        currentRow = sum(row)
        if (currentRow <= prevRow):
           return False
        prevRow= currentRow
    else:
        return True

answered Dec 16, 2017 at 15:30

oBit91

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2 Comments

Siyah Over a year ago

Ah, even though it's a bit longer than other answers, I like the clear and concise way of doing it. Thank you very much!

oBit91 Over a year ago

Glad to have helped, just wanted to clarify that schwobaseggl's answer is more 'Pythonic' whilst mine is more vanilla. FYI.

Elisha · Accepted Answer · 2017-12-16 15:32:14Z

3

It is enough to store the latest sum in order to get an answer:

def increasing(m):
    last_sum = -float('inf')
    for row_sum in map(sum, m):
        if row_sum < last_sum:
            return False
        last_sum = row_sum

    return True

edited Dec 16, 2017 at 15:32

answered Dec 16, 2017 at 15:29

Elisha

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3 Comments

Siyah Over a year ago

What does - float('inf') even do? I don't get it.

Elisha Over a year ago

@Siyah, the expression is equivalent to "minus infinity". Here, it is used to avoid special treatment to the first row.

Siyah Over a year ago

Interesting. Never heard of that before. Thanks @Elisha!

Joe Iddon · Accepted Answer · 2017-12-16 15:37:01Z

2

You could first create a list of the sums of the rows, and then check whether that list is increasing.

def increasing(m):
    sums = [sum(r) for r in m]
    return all(sums[i] < sums[i+1] for i in range(len(m)-1))

and we can test this with:

m1  = [[1, 3, 2, 5],
       [7, 9, 4, 1],
       [3, 5, 6, 9]]

m2  = [[2, 8, 4, 1],
       [6, 2, 8, 5],
       [8, 4, 2, 1]]

which produces the correct results:

>>> increasing(m1)
True
>>> increasing(m2)
False

answered Dec 16, 2017 at 15:37

Joe Iddon

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Comments

Danii-Sh · Accepted Answer · 2017-12-16 15:30:05Z

1

just simply do

row[0]+row[1]+row[2]+row[3]

for summation process and the problem of not knowing line numbers is handled by iterating on rows, which you will not have any problem

answered Dec 16, 2017 at 15:30

Danii-Sh

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1 Comment

Siyah Over a year ago

I don't get how that works. When I do that, it just shows me the first numbers in every row, which is not what I want.

muyns · Accepted Answer · 2018-05-07 09:13:48Z

0

from sklearn import preprocessing

import csv, sys

with open("m.txt") as f:

reader = csv.reader(f)
next(reader) # skip header
data = [r for r in reader]
data.pop(0)
print(type(data))
a=np.asarray(data)
print(np.nanvar(a,ddof=1))

answered May 7, 2018 at 9:13

muyns

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