mutate() for new columns in R Programming - Step-by-Step Execution

Concept Flow - mutate() for new columns

Start with data frame

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Call mutate()

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Define new column(s)

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Calculate values for new column(s)

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Add new column(s) to data frame

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Return updated data frame

mutate() takes a data frame and adds new columns by calculating values, then returns the updated data frame.

Execution Sample

R Programming

library(dplyr)
data <- data.frame(x = 1:3, y = 4:6)
data <- mutate(data, z = x + y)

Adds a new column 'z' to data by summing columns 'x' and 'y'.

Execution Table

Step	Action	Evaluation	Result
1	Start with data frame	data has columns x and y	x: 1,2,3; y: 4,5,6
2	Call mutate(data, z = x + y)	Calculate z for each row	z: 5,7,9
3	Add column z to data	New data frame has x, y, z	x:1,2,3; y:4,5,6; z:5,7,9
4	Return updated data frame	data now includes z	data with new column z

💡 All rows processed; new column z added successfully

Variable Tracker

Variable	Start	After mutate	Final
data$x	1,2,3	1,2,3	1,2,3
data$y	4,5,6	4,5,6	4,5,6
data$z	N/A	5,7,9	5,7,9

Key Moments - 2 Insights

Why does the new column 'z' appear after mutate()?

Because mutate() calculates 'z' using existing columns 'x' and 'y' and adds it to the data frame, as shown in step 3 of the execution table.

Does mutate() change the original data frame immediately?

No, mutate() returns a new data frame with the added column. You must assign it back to a variable, like 'data <- mutate(...)', as shown in the code sample.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'z' after step 2?

A 5,7,9

B 1,2,3

C 4,5,6

D N/A

💡 Hint

Check the 'Evaluation' column in step 2 of the execution table where z is calculated.

At which step is the new column 'z' added to the data frame?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look at the 'Action' column describing when the column is added.

If you forget to assign mutate() result back to 'data', what happens?

A data gets updated automatically

B An error occurs

C data remains unchanged

D The new column is added temporarily

💡 Hint

Refer to the key moment about assignment after mutate().

Concept Snapshot

mutate(data, new_col = expression)
- Adds new_col to data by evaluating expression
- Uses existing columns in expression
- Returns updated data frame
- Must assign result to keep changes
- Great for creating calculated columns

Full Transcript

The mutate() function in R adds new columns to a data frame by calculating values from existing columns. It takes the data frame and new column definitions, computes the values row by row, and returns a new data frame with the added columns. You must assign the result back to a variable to keep the changes. For example, mutate(data, z = x + y) adds a column z that sums x and y. The execution table shows each step: starting with the original data, calculating z, adding z to the data frame, and returning the updated data. Variable tracking shows how the new column z changes from not existing to having values. Remember, mutate does not change the original data frame unless you assign the result back.