Grouping Numeric Data

To categorize numeric data into groups, you can use the cut() function in R, which assigns each number to a category based on specified intervals. For instance, if you have a continuous variable like height, you can categorize individuals as 'tall', 'medium', or 'short' based on height ranges.

Here's how you can use it:

r
cut(x, breaks, labels = NULL, right = TRUE, ordered_result = FALSE, ...)

Among the parameters listed, these are crucial for categorizing data:

x is the numeric vector to be categorized;
breaks can be an integer specifying the number of intervals or a vector of cut points;
labels provide names for the categories;
right indicates if the intervals should be closed on the right;
ordered_result determines if the resulting factors should have an order.

To create three categories, set breaks to 3 or provide a vector with four cut points to form three intervals, for instance (a,b], (b,c], (c,d].

# Vector of heights

heights <- c(170, 165, 195, 172, 189, 156, 178, 198,

157, 182, 171, 184, 163, 176, 169, 153)

# Convert into factor by cutting into intervals

heights_f <- cut(heights, breaks = c(0, 160, 190, 250),

labels = c('small', 'medium', 'tall'), ordered_result = T)

heights_f # Output the factor variable


              1234567
            
# Vector of heights
heights <- c(170, 165, 195, 172, 189, 156, 178, 198,
            157, 182, 171, 184, 163, 176, 169, 153)
# Convert into factor by cutting into intervals
heights_f <- cut(heights, breaks = c(0, 160, 190, 250), 
                labels = c('small', 'medium', 'tall'), ordered_result = T)
heights_f # Output the factor variable

For our example of categorizing height, we choose c(0, 160, 190, 250) for breaks to divide the data into three groups: (0, 160], (160, 190], and (190, 250]. We also set ordered_result to TRUE to define a logical order among categories (e.g., short < medium < tall).

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Given a vector of numerical grades, here's how to categorize them as factor levels:
- [0, 60) - F;
- [60, 75) - D;
- [75, 85) - C;
- [85, 95) - B;
- [95, 100) - A.
Create a variable grades_f that stores the factor levels with the specified breaks and labels, considering the ordering, and use right = FALSE to include the left boundary of the intervals;
- breaks - c(0, 60, 75, 85, 95, 100);
- labels - c('F', 'D', 'C', 'B', 'A');
- ordered_result - TRUE (to order the factor values);
- right - FALSE (to include the left boundary of an interval, not the right).
Output the contents of grades_f.