Data Wrangling - Part 2

Lecture 6

Dr. Elijah Meyer

Duke University
STA 199 - Spring 2023

September 14, 2022

Checklist

– Clone ae-04

– HW-1 Due Tonight on Gradescope

Announcements

– AE’s are being graded

– Keep posting on Slack

– Feedback for Lab-0 is live

Goals for today

– Continue practicing with dplyr functions

– Change variable types

– Understand variable types

Warm up

Identify which dplyr functions chooses rows or changes columns of an exsisting data set

– filter()

– select()

– slice()

– arrange()

Warm up

– filter() - row

– select()

– slice()

– arrange()

Warm up

– filter() - row

– select() - column

– slice()

– arrange()

Warm up

– filter() - row

– select() - column

– slice() - row

– arrange()

Warm up

– filter() - row

– select() - column

– slice() - row

– arrange() - row

Single pipeline

What is a single pipeline?

– “Do everything in one go”

Ex.

mtcars |>
  mutate(cyl = factor(cyl)) |>
  ggplot(
    aes(x = mpg, y = wt, fill = cyl)
  ) +
  geom_point()

What isn’t a single pipeline?

Ex.

mtcars <- mtcars |>
  mutate(cyl = factor(cyl))

mtcars |>
  ggplot(
    aes(x = mpg, y = wt, fill = cyl)
  ) +
  geom_point()

Types of variables

Types of variables

Type is how an object is stored in memory.

– glimpse is a great way to check data types

– Can also use typeof()

Examples

– glimpse(mtcars)

– typeof(mtcars$mpg)

Types of variables

Some of the types of variables include:

– “logical”

– “integer”

– “double”

– “character”

– “factor”

logical

– logi in glimpse

– The logical data type in R is also known as boolean data type. It can only have two values: TRUE and FALSE.

– as.logical can turn a variable into a logical. False = 0; True everything else

integer

– int in glimpse

– Integers are whole numbers (those numbers without a decimal point)

– as.integer can turn a double into an integer. Forces 22.8 -> 22.

double

– dbl in glimpse

– Real numbers (can include decimals)

– as.doublecan force a column to be a double. Identical to as.numeric.

character

– chr in glimpse

– Character string (text)

– as.character attempts to coerce its argument to character type

factor

– fct in glimpse

– Factor in R is also known as a categorical variable that stores both string and integer data values as levels.

– factor attempts to coerce its argument to factor type

Why this matters

– Plotting

– Summary statistics

General takeaways

– Can you identify variable types

– Often need to turn something into a factor to make it categorical

– Often need to turn something into a double (numeric) to make it quantitative

More on this later

ae-04

Wrap up

– Data types matter. Get in the habit of checking them at the beginning of analysis

– Have the tools to create new variables, calculate summary statistics, etc. that accompany strong visualizations

🔗 sta199-s23-2.github.io