3.5 CHANGING MISLEADING FIELD VALUES
The field days_since_previous is a count of the number of days since the client was last contacted from a previous campaign. This field is clearly numeric, so we can look at a histogram4 of days_since_previous provided by R in Figure 3.1. Note that most of the data values are near 1000, with a minority of values near zero. It turns out that the database administrator used the code 999 to represent customers who had not been contacted previously. Thus, we need to change the field value 999 to missing, which is done as follows in Python and R.
![Image described by caption.](https://static.packt-cdn.com/products/9781119526810/graphics/images/c03f001.gif)
Figure 3.1 Histogram from R of days_since_previous, with most values near 1000.
3.5.1 How to Change Misleading Field Values Using Python
If you did not open the pandas package or read in the data set, as described in the previous Python section, do so now. We also need to import the numpy package for this section.
import numpy as np
We need to identify all records with days_since_previous value of 999 and...