# If else statement and selection of certain data only

To describe my problem in easy way is, for example, I have frequency from [1,2,3,4,5,6] and data = [4,7,2,1,4,9] for each of the frequency. I need to make summation only data with frequency from 3-5Hz in MATLAB. How do I want to write code to satisfy my problem? Below is my trial to do the program code but not working.

```f=[1,2,3,4,5,6];
data = [4,7,2,1,4,9];

if 3<=f<=5
sumdata=sum(data);
else
end
```

You can use

```f=[1,2,3,4,5,6];
data = [4,7,2,1,4,9];
validData = data(f <= 5 & f >= 3);
result = sum(validData);
```

Try :

```f=[1,2,3,4,5,6];
data = [4,7,2,1,4,9];

sumdata = sum(data(3 <= f & f <= 5));
```

The operation: 3 <= f & f <= 5 give you a logical matrix of the value that met the conditions.

```>> 3 <= f & f <= 5
ans =
0     0     1     1     1     0
```

You can then use this logical matrix to get only the value corresponding to valid index in you data : data(3 <= f & f <= 5) and then, sum them : sum(data(3 <= f & f <= 5)).

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