# 问题内容:

I have a matrix and I want to return an array containing as elements the sum of each row elements of the matrix.

int [] sum;

for (var i = 0; i < m; i++)
{
for (var j = 0; j < result.Pages[i].Actual.Count; j++)
{
sum[i] += result.Pages[i].Actual[j];
}

}


This is how I tried to do it but seems it is not working. Any ideas?

## 问题评论:

you can simply get the length of each array dimension and use that to determine how many times to loop. google.co.uk/…
– user3654571
48 mins ago
what is Pages ? a List ?

# 答案:

## 答案1:

Use var m = a.GetLength(0); to get number of rows, and var n = a.GetLength(1); to get number of columns.

## 答案2:

now that looks like a different story after you edit:

Actually the first problem would be a NullreferenceException because int[]sum is not initialized!

Anyway, so it seems that you have an array of arrays. In this case you would need the Length of the Pages array to save your results. The first loop iterates over it using i and will run until result.Pages.Length. For each i you have correctly implemented a second loop where you sum up the result.

int [] sum = new int[result.Pages.Length];

for (var i = 0; i < result.Pages.Length; i++)
{
for (var j = 0; j < result.Pages[i].Actual.Length; j++)
{
sum[i] += result.Pages[i].Actual[j];
}
}


If you collections are List‘s then you need to use Count instead of Length

The Linq solution would look like this:

int [] sum = result.Pages.Select(x=>x.Sum()).ToArray();


EDIT:

double? means that you have a nullable data type. This is different from the normal double. Furthermore the default value will be null That means that you need to change the initialize the value at position i.

double? [] sum = new double?[result.Pages.Length];

for (var i = 0; i < result.Pages.Length; i++)
{
sum[i] = 0;
for (var j = 0; j < result.Pages[i].Actual.Length; j++)
{
sum[i] += result.Pages[i].Actual[j];
}
}


## 答案评论:

thanks for your answer. it seems clear now. I only have one issue, the data is in double? format or that the error I’m get. I changed sum from int to double but still now effect
– user3654571
39 mins ago
@user3654571 “or that the error I’m get. ” I don’t see any error… does it have an error message? you really should post the code that you are testing, otherwise we keep playing a guessing game
this is the code and the error: pastebin.com/W8bhe2tW
– user3654571
34 mins ago
@user3654571 double? means that you have a nullable data type. This is different from the normal double. Furthermore the default value will be null That means that you need to change the initialize the value at position i

## 答案3:

I expected this to become a pretty one line linq approach – sorry but at least it’s one line

int[,] items = { { 1, 2, 3 }, { 2, 3, 4 }, { 3, 4, 5 } };
int[] sum = Enumerable.Range(0, items.GetLength(0))
.Select(x => Enumerable.Range(0, items.GetLength(1))
.Sum(y => items[x,y])).ToArray();
//sum[] == {6,9,12}


for-loop appraoch

int[,] items = { { 1, 2, 3 }, { 2, 3, 4 }, { 3, 4, 5 } };
int[] sum = new int[items.GetLength(0)];
for (int i = 0; i < items.GetLength(0); i++)
for (int j = 0; j < items.GetLength(1); j++)
sum[i] += items[i, j];

//sum[] == {6,9,12}


## 原文地址：

https://stackoverflow.com/questions/47755761/save-the-sum-of-each-row-of-a-matrix-into-an-array

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