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Overview

Questions

  • How can I manipulate a data frame?

Objectives

  • Use the dplyr package to manipulate data frames.
  • Remove rows with NA values
  • Append two data frames.
  • Understand what a factor is.
Data Frames Figure
Figure 1.1 Detailed description of the image and its contents for accessibility purposes.
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Information

The shell is a program that enables us to send commands to the computer and receive output. It is also referred to as the terminal or command line.

Some computers include a default Unix Shell program. The steps below describe some methods for identifying and opening a Unix Shell program if you already have one installed. There are also options for identifying and downloading a Unix Shell program, a Linux/UNIX emulator, or a program to access a Unix Shell on a server.

If none of the options below address your circumstances, try an online search for: Unix shell [your computer model] [your operating system].

This is what code directly from pandoc looks like

drop <- names(cats) %in% c("age")
cats[,!drop]

This has been a markdown document with some code

           coat weight likes_string
1        calico    2.1            1
2         black    5.0            0
3         tabby    3.2            1
5 tortoiseshell    3.3            1

R

drop <- names(cats) %in% c("ageageageageageageageageageageageageageageageageageageageageageageageageage")
cats[,!drop]

drop <- names(cats) %in% c("age")
cats[,!drop]

OUTPUT


           coat weight likes_string
1        calico    2.1            1
2         black    5.0            0
3         tabby    3.2            1
5 tortoiseshell    3.3            1

ERROR


Error in data.frame(..., check.names = FALSE): arguments imply differing number of rows: 3, 2

Challenge

Let’s imagine that 1 cat year is equivalent to 7 human years.

Create a vector called human_age by multiplying cats$age by 7. Convert human_age to a factor. Convert human_age back to a numeric vector using the as.numeric() function. Now divide it by 7 to get the original ages back. Explain what happened.

INPUT


1.  human_age <- cats$age * 7
2.  human_age <- factor(human_age). as.factor(human_age) works just as well.
3.  as.numeric(human_age) yields 1 2 3 4 4

because factors are stored as integers (here, 1:4), each of which is associated with a label (here, 28, 35, 56, and 63). Converting the factor to a numeric vector gives us the underlying integers, not the labels. If we want the original numbers, we need to convert human_age to a character vector (using as.character (human_age)) and then to a numeric vector (why does this work?). This comes up in real life when we accidentally include a character somewhere in a column of a .csv file supposed to only contain numbers, and forget to set stringsAsFactors=FALSE when we read in the data.

This is the second item's accordion body. It is hidden by default, until the collapse plugin adds the appropriate classes that we use to style each element. These classes control the overall appearance, as well as the showing and hiding via CSS transitions. You can modify any of this with custom CSS or overriding our default variables. It's also worth noting that just about any HTML can go within the .accordion-body, though the transition does limit overflow.
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Checklist
  • Use the dplyr package to manipulate data frames.
  • Remove rows with NA values
  • Append two data frames.
  • Understand what a factor is.
Testimonial

The shell is a program that enables us to send commands to the computer and receive output. It is also referred to as the terminal or command line.

Some computers include a default Unix Shell program. The steps below describe some methods for identifying and opening a Unix Shell program if you already have one installed. There are also options for identifying and downloading a Unix Shell program, a Linux/UNIX emulator, or a program to access a Unix Shell on a server.

If none of the options below address your circumstances, try an online search for: Unix shell [your computer model] [your operating system].

Discussion

The shell is a program that enables us to send commands to the computer and receive output. It is also referred to as the terminal or command line.

Some computers include a default Unix Shell program. The steps below describe some methods for identifying and opening a Unix Shell program if you already have one installed. There are also options for identifying and downloading a Unix Shell program, a Linux/UNIX emulator, or a program to access a Unix Shell on a server.

If none of the options below address your circumstances, try an online search for: Unix shell [your computer model] [your operating system].

Prerequisites

The shell is a program that enables us to send commands to the computer and receive output. It is also referred to as the terminal or command line.

Some computers include a default Unix Shell program. The steps below describe some methods for identifying and opening a Unix Shell program if you already have one installed. There are also options for identifying and downloading a Unix Shell program, a Linux/UNIX emulator, or a program to access a Unix Shell on a server.

If none of the options below address your circumstances, try an online search for: Unix shell [your computer model] [your operating system].

Key Points

The shell is a program that enables us to send commands to the computer and receive output. It is also referred to as the terminal or command line.

Some computers include a default Unix Shell program. The steps below describe some methods for identifying and opening a Unix Shell program if you already have one installed. There are also options for identifying and downloading a Unix Shell program, a Linux/UNIX emulator, or a program to access a Unix Shell on a server.

If none of the options below address your circumstances, try an online search for: Unix shell [your computer model] [your operating system].