emax February 2016
### How to find two consecutive positive-negative values in an array?

I have the following array:

```
X
array([ 3.5, -3, 5.4, 3.7, 14.9, -7.8, -3.5, 2.1])
```

For each values of `X`

I know its recording time `T`

. I want to find the indexes between two consecutive positive-negative or viceversa. Concluding I would like an array like

```
Y = array([ T(1)-T(0), T(2)-T(1), T(5)-T(4), T(7)-T(6)])
```

Perhaps iterating over the array in a list comprehension would work for you:

```
In [35]: x=np.array([ 3.5, -3, 5.4, 3.7, 14.9, -7.8, -3.5, 2.1])
In [36]: y=np.array([b-a for a,b in zip(x, x[1:]) if (a<0) != (b<0)])
In [37]: y
Out[37]: array([ -6.5, 8.4, -22.7, 5.6])
```

I apparently didn't understand the question completely. Try this instead:

```
In [38]: X=np.array([ 3.5, -3, 5.4, 3.7, 14.9, -7.8, -3.5, 2.1])
In [39]: T=np.array([ 0, 0.1, 2, 3.5, 5, 22, 25, 50])
In [40]: y=np.array([t1-t0 for x0,x1,t0,t1 in zip(X, X[1:], T, T[1:]) if (x0<0) != (x1<0)])
In [41]: y
Out[41]: array([ 0.1, 1.9, 17. , 25. ])
```

Asked in February 2016

Viewed 2,413 times

Voted 12

Answered 1 times

Viewed 2,413 times

Voted 12

Answered 1 times