User-defined functions (solutions)

Primary exercises

For weight and height measurements we have the metric (cm,kg) and imperial (inch,lbs) systems. The relation between the measurements in different systems is (1 kg = 2.2 lbs) and (1 inch = 2.54 cm). Write the following unit conversion functions:
- cm2meter : convert cm to meter
- lbs2kg : convert weight unit pound to kg
- inch2cm : convert inch to cm

# Some example calls to the functions:
> inch2cm(70)
[1] 177.8
> lbs2kg(10)
[1] 4.545455
> cm2m(190)
[1] 1.9

cm2m    <- function(x) x*0.01  # cm to meter
lbs2kg  <- function(x) x/2.2   # pound to kg
inch2cm <- function(x) x*2.54  # inch to cm

Write a function for the survey dataset to report a summary on average pulse and the number of individuals in the given age range. Call it ageRangePulseSummary and it should take 3 arguments, the survey data, minimum age and maximum age, for example:

ageRangePulseSummary <- function(x, lowerBound,upperBound) {
  x %>% filter(age >= lowerBound & age < upperBound) %>% 
    summarise(meanpulse=mean(pulse, na.rm = TRUE),individuals=n())
}

ageRangePulseSummary(survey, 16,17)

# A tibble: 1 × 2
  meanpulse individuals
      <dbl>       <int>
1      76.2           4

Take the function weightRangeSummary in the lecture notes, make the necessary update such that it includes the weight intervals.

weightRangeSummary <- function(x, lowerBound,upperBound) {
  x %>% filter(weight >= lowerBound & weight < upperBound) %>% 
    summarise(meanHeight=mean(height),
              increasedPulse=sum(pulse1<pulse2, na.rm = TRUE),
              weightLowerBound=lowerBound,
              weightUpperBound=upperBound,
              individuals=n())
}

Extra exercises

Write a function odd which takes a number as argument and returns a logical TRUE if the number is an odd number and FALSE otherwise. A whole number is odd when it is not integer divisible by 2. We can check whether a number is divisible by 2 by using the integer division remainder operator %%, known as modulo. The operator returns the remainder of integer (whole number) division:

9 %% 2  # remainder after dividing 9 by 2

[1] 1

8 %% 2  # remainder after dividing 8 by 2

[1] 0

1:10 %% 2 # remainder after dividing 1..10 by 2

 [1] 1 0 1 0 1 0 1 0 1 0

As you can see the outcome is 0 if the number at the left is integer divisible by 2 and 1 if not. We can use this fact to test whether a number is odd, i.e. not divisible by 2.

odd <- function(x) {
  x %% 2 != 0
}

odd(31)

[1] TRUE

odd( x = 6 ) # more readable than '6 %% 2 != 0'

[1] FALSE

Write the function even which tests whether a number is even.

even <- function(x) {
  x %% 2 == 0
}
# Alternatively: define the even function in terms of the 'negated' odd function.

even <- function(x) {
  ! odd(x)
}

Write a function divisible which given values x and m tests whether x is integer divisible by m.

divisible <- function(x,m) {
  x %% m == 0
}

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