## Time for action – balancing volume

In other words, we need to multiply the sign of the close price and the volume. In this section, we look at two approaches to this problem: one using the NumPy `sign()` function and the other using the NumPy `piecewise()` function.

1. Load the BHP data into a close and volume array:

`c, v=np.loadtxt('BHP.csv', delimiter=',', usecols=(6, 7), unpack=True)`

Compute the absolute value changes. Calculate the change of the closing price with the `diff()` function. The `diff()` function computes the difference between two sequential array elements and returns an array containing these differences:

```change = np.diff(c)
print("Change", change)```

The changes of the close price are shown as follows:

```Change [ 1.92 -1.08 -1.26  0.63 -1.54 -0.28  0.25 -0.6   2.15  0.69 -1.33  1.16
1.59 -0.26 -1.29 -0.13 -2.12 -3.91  1.28 -0.57 -2.07 -2.07  2.5   1.18
-0.88  1.31  1.24 -0.59]
```
2. The NumPy `sign()` function returns the signs for each element in an array. -1 is returned for a negative number...