Calculating the absolute value of a number is one of the various mathematical
functions available to use on your data.
If you take a close look at the Number_of_rentals column, you will
notice that some of the numbers have a negative value.
These cells are not marked as incorrect in the quality bar because they still fit the
semantic type automatically set as integer
. Nevertheless, this is
unusable data. As a consequence, you are going to apply a function to remove the
negative sign for all these numbers.
To calculate the absolute value of your data, proceed as follows:
Procedure

Click the header of the Number_of_rentals column to
select its content.
In the statistics box, you can clearly see that some values range between
10 and 0.

In the vertical bar chart at the bottom right of the screen, click the first
bar from the left.
This bar represents all the occurrences of the values that are equal or below
0.
A filter has now been applied on your data. Your preparation now only
displays the lines with a value equal or below zero for the number of
rentals. You can now apply a function only on those cells.

Under the functions list, in front of Apply changes to:,
select the Filtered Lines radio button.

In the functions list, click Calculate Absolute
Value.
All the negative values have been converted.

To clear the filter, simply click the x icon, on the
right of the filter.
Results
Your preparation now displays all your data
again. If you take another look at the statistics box for the
Number_of_rentals column, you can see that the minimum value is now
0 instead of
10. You have thus improved the quality and usability of your
data.