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Suppose that I have a 2×2 array of the form:

[a, b

c, d]

Here a, b, c and d are numbers.

How can I calculate the column-wise sum in Julia? The result should be the column vector:

[a + b

c + d].

### >Solution :

Assume your data is

```
mat = [11 12; 21 22 ]
2×2 Matrix{Int64}:
11 12
21 22
```

the column sum is given by

```
sum( mat , dims = 2 )
2×1 Matrix{Int64}:
23
43
```

and you can get the row sum via `sum( mat , dims = 1 )`

. To produce a vector from that you can do `vec( sum( mat , dims = 2 ) )`

which gives `(2,)`

that is a vector