8 Appendix - Understanding Boolean Operators in the Context of filter()

In the Chapter 5, I brushed over what the operators < and &, and | meant and what they were actually doing in R. Each of these operators are known as Boolean operators in R.

Boolean operators are logical operators used in programming to combine or modify conditions, resulting in either TRUE or FALSE outcomes. In the context of data cleaning in R, Boolean operators help us construct conditions to select specific rows from a data frame based on certain criteria. When using filter(), R evaluates each row in the data frame against the specified conditions, determining whether each row meets the criteria and should be retained or not.

8.1 How Boolean Operators Work:

• Logical AND (&): The & operator evaluates to TRUE only if both conditions on either side of the operator are TRUE. In the context of filter(), rows are retained if they satisfy all conditions joined by &. For example, filter(df, x > 5 & y < 10) will retain rows where x is greater than 5 and y is less than 10.

• Logical OR (|): The | operator evaluates to TRUE if at least one of the conditions on either side of the operator is TRUE. In the context of filter(), rows are retained if they satisfy any of the conditions joined by |. For example, filter(df, x > 5 | y < 10) will retain rows where x is greater than 5 or y is less than 10.

• Logical NOT (!): The ! operator negates a condition, converting TRUE to FALSE and vice versa. In the context of filter(), ! can be used to exclude rows that satisfy a particular condition. For example, filter(df, !(x == 5)) will exclude rows where x equals 5.

8.1.1 Understanding R’s Evaluation Process:

When applying filter() with Boolean operators, R sequentially evaluates each row in the data frame against the specified conditions. If a row satisfies all conditions joined by &, or any condition joined by |, it is retained in the filtered data frame. Rows that do not meet the specified criteria are excluded from the output.

The following table summarises the main Boolean operators we would use in R

Operator/Condition	Description	Example
==	Checks if two values are equal.	x == 5 evaluates to TRUE if x equals 5.
!=	Checks if two values are not equal.	x != 5 evaluates to TRUE if x does not equal 5.
>	Checks if one value is greater than another.	x > 5 evaluates to TRUE if x is greater than 5.
<	Checks if one value is less than another.	x < 5 evaluates to TRUE if x is less than 5.
>=	Checks if one value is greater than or equal to another.	x >= 5 evaluates to TRUE if x is greater than or equal to 5.
<=	Checks if one value is less than or equal to another.	x <= 5 evaluates to TRUE if x is less than or equal to 5.
&	Logical AND operator; evaluates to TRUE only if both conditions are TRUE.	(x > 5) & (y < 10) evaluates to TRUE if x is greater than 5 AND y is less than 10.
|	Logical OR operator; evaluates to TRUE if at least one condition is TRUE.	(x > 5) \| (y < 10) evaluates to TRUE if x is greater than 5 OR y is less than 10.
!	Logical NOT operator; negates a condition.	!(x == 5) evaluates to TRUE if x is not equal to 5.