HalfPintBoy - 1 year ago 75

Python Question

Having numpy array like that:

`a = np.array([35,2,160,56,120,80,1,1,0,0,1])`

I want to subtract custom value (for example, 5) from first element of the array. Basically it can be done like:

`a[0] - 5`

But how can I apply this result to the initial array and replace the first value with the answer?

Thanks!

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Answer Source

You can use:

`a[0] `**-=** 5 # use -=

This will turn `a`

into:

```
>>> a = np.array([35,2,160,56,120,80,1,1,0,0,1])
>>> a[0] -= 5
>>> a
array([ 30, 2, 160, 56, 120, 80, 1, 1, 0, 0, 1])
```

For most operations (`+`

, `-`

, `*`

, `/`

, etc.), there is an "inplace" equivalent (`+=`

, `-=`

, `*=`

, `/=`

, etc.) that will apply that operation with the right operand and store it back.

Note that if you want to subtract *all* elements, you should not use a Python `for`

loop, there are more efficient ways for that.

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