CSC121 - R Console
Wednesday January 24th
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> # Last time, I wanted to mention, that we can get a new vector by removing an element from an existing vector
> # Example: remove the element at index 3
> v <- c(1,2,3,4,5)
> # we use negative indexes
> v[-3]
[1] 1 2 4 5
> v
[1] 1 2 3 4 5
> v <- v[-3]
> v
[1] 1 2 4 5
> v[c(-2, -3)]
[1] 1 5
> v
> # remember that we can only change elements of vectors in place like this:
[1] 1 2 4 5
> v[1] <- 4
> v
[1] 4 2 4 5
> 
> # Back to logical values
> # Last time we introduced TRUE and FALSE as logical values
> # These values are used to evaluate the truth values of statements
> 12 > 5
[1] TRUE
> 1 + 2 == 5
[1] FALSE
> # Let's now combine numerical vectors with logical values
> 
> # Consider the vector v:
> v <- c(1:5)
> v
[1] 1 2 3 4 5
> # We saw that the logical comparisons like 4 > 3 give us a logical value (TRUE)
> # What if we do a comparison on the entire vector?
> v > 3
[1] FALSE FALSE FALSE  TRUE  TRUE
> # We get a vector of logical values that gives us a comparison on every element of v, and puts it in the corresponding index
> # What will these give:
> v <= 4
[1]  TRUE  TRUE  TRUE  TRUE FALSE
> v == 2
[1] FALSE  TRUE FALSE FALSE FALSE
> v != 1
[1] FALSE  TRUE  TRUE  TRUE  TRUE
> 
> # Indexing vectors using logical values
> # We can create a slice of a vector by using logial vectors as the index!
> v
[1] 1 2 3 4 5
> v[c(TRUE, FALSE, FALSE, TRUE, FALSE)]
[1] 1 4
> # It picked out the indexes that are TRUE in the logical vector (index 1 and 4)
> # Since we can do a comparison operation ot get a logical vector, we can index v based on some condition
> v > 3
[1] FALSE FALSE FALSE  TRUE  TRUE
> v[v > 3]
[1] 4 5
> v[v != 2]
[1] 1 3 4 5
> # Let's revisit our question from last time:
> # Given v <- c(1:10), how do we pick out the even numbers of v?
> v <- c(1:10)
> v
 [1]  1  2  3  4  5  6  7  8  9 10
> 2 %% 2
[1] 0
> 1 %% 2
[1] 1
> v[v %% 2 == 0]
[1]  2  4  6  8 10
> v[v %% 2 == 1]
[1] 1 3 5 7 9
> # If the logical vector we're indexing at is smaller than the length of the vector we're indexing, it will just repeat the logical index vector 
> v
 [1]  1  2  3  4  5  6  7  8  9 10
> v[c(TRUE, FALSE, TRUE)]
[1]  1  3  4  6  7  9 10
> p <- c(1,4,7,10)
> q <- c(44,5,3,26)
> c(q[q < 7], p[p >= 10])
[1]  5  3 10
> 
> # There are some built-in R functions that return logical values
> # is 4.3 a double?
> is.double(4.3)
[1] TRUE
> is.double(4)
[1] TRUE
> is.double(as.integer(4))
[1] FALSE
> is.integer(5.4)
[1] FALSE
> is.logical(TRUE)
[1] TRUE
> is.logical(24234)
[1] FALSE
> # Often you will name logical variables with words like 'is', or 'has'
> isRaining <- FALSE
> # if someone has a bike:
> hasBike <- TRUE
>
> # Running our if-statement functions
> source('~/Desktop/W3/jan24_lecture/if_statement_functions.R')
> TicketPrice(3)
[1] 4.25
> TicketPrice(34)
[1] 7.5
> TicketPrice(109)
[1] 4.75
> source('~/Desktop/W3/jan24_lecture/if_statement_functions.R')
> FlightPrice(500, FALSE)
[1] 500
> FlightPrice(500, TRUE)
[1] 900
> source('~/Desktop/W3/jan24_lecture/if_statement_functions.R')
> NumberFun(2,2)
[1] 1
> NumberFun(2,1)
[1] 2
> NumberFun(3,1)
[1] 3
> NumberFun(3,5)
[1] 3
> NumberFun(3,6)
[1] 3
> source('~/Desktop/W3/jan24_lecture/if_statement_functions.R')
> LaptopPrice(FALSE, FALSE)
[1] 1299
> LaptopPrice(TRUE, FALSE)
[1] 899
> LaptopPrice(FALSE, TRUE)
[1] 1799
> LaptopPrice(TRUE, TRUE)
[1] 1399