Variables (solutions)

Primary exercises

Create a new variable.
Make a variable heightInMeters that contains your height expressed in meters.
Print the variable.
Find the variable and its value in the Environment pane.

heightInMeters <- 1.75
heightInMeters

[1] 1.75

Use a variable in an expression.
Use the variable heightInMeters to calculate your height in cm.
Calculate the height in cm once again and store the result in a variable heightInCentimeters.
Show/print heightInCentimeters.

heightInMeters * 100

[1] 175

heightInCentimeters <- heightInMeters * 100
heightInCentimeters

[1] 175

Change a value of a variable.
Increase the height stored in heightInMeters by 0.1m.
Check whether the value of the variable indeed changed.
Has the value of heightInCentimeters also changed? Why?

heightInMeters <- heightInMeters + 0.1
heightInMeters

[1] 1.85

heightInCentimeters      # not changed, for change assignment is needed

[1] 175

Typo in variable name.
Observe the error shown when you try to print a variable but you make a typo in the variable name.

height.in.meters      # Error: object 'height.in.meters' not found

Error in eval(expr, envir, enclos): object 'height.in.meters' not found

Extra exercises

The pi.
pi is a variable built in R. Use it to calculate the area of a circle of radius 2.0.

radius <- 2.0
pi * radius^2

[1] 12.56637

Various assignment operators.
In addition to <- R has other assignment operators = (equivalent to <-) and -> (the variable name on the right side).
Use each of these operators in an assignment. When do you think -> might be useful?

x <- 1
x

[1] 1

y = 2
y

[1] 2

3 -> z
z

[1] 3

1 + 1/(
  1 + 1/(
    1 + 1/(
      1 + 1/(
        1
      )
    )
  )
) -> u # right arrow is handy while typing and when the cursor is at the end of a long expression,
u      # but makes code less readable (do not use in production code)

[1] 1.6

List defined variables; remove a variable.
Use ls() to find what variables are currently known. Compare the output with the content of the Environment pane.
Define a new variable xyz = 5. Find how to use rm to remove the variable from the current environment.

xyz <- 5
rm( xyz )
xyz

Error in eval(expr, envir, enclos): object 'xyz' not found

Restart R session.
(Warning: you are going to loose all what you have typed).
First define several variables (so you can see some in the Envinroment pane).
Try Restart R option from the Session menu.
What happened? What happened to the variables?

# Restarting brings R to the initial state.
# Note, that in menu "Tools/Global options" it is possible to enable:
#   "Restore .RData into workspace at startup".
# When this option is enabled some variables might be present when R is restarted.
# This might lead to unreproducible results so we suggest to disable that option.

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