Appendix B — DO NOT use parentheses when they are clearly not necessary.
#####################################################################.# In general, DO NOT use parentheses when they are clearly not necessary. ##### It shows poor knowledge of the R language. #####################################################################.# Don't do this! - you never need parentheses around a single valueseq((1), (3))
[1] 1 2 3
# Don't do this! - unnecessary parentheses(seq(1,3))
[1] 1 2 3
# Don't do this! - you never need parentheses around a single argumentx=2seq(1,(3+x)) # do not put parentheses around a single argument
[1] 1 2 3 4 5
# This is the way to do it.seq(1 , 3+x) # better!
[1] 1 2 3 4 5
#####################################################################.# It is acceptable to use extra parentheses when they are used to # clarify the order of operations. Not everyone knows the order of # operations by heart and this can make your code more readable.#####################################################################.# For example:10-(2:10)
[1] 8 7 6 5 4 3 2 1 0
# is very different from (10-2):10
[1] 8 9 10
# The following (without the parentheses)10-2:10
[1] 8 7 6 5 4 3 2 1 0
# is the same as 10-(2:10) as the order of operations lists the# colon operator (:) before the subtraction operator (-)# ( see ?Syntax )## Therefore, I'd accept 10-(2:10) even thought strictly speaking the # parentheses are not necessary as the parentheses help to clarify the# order of operations.############################################################################.# QUESTION: The vector, x, contains at lest 3 values.# Write a command to show the last 3 values in the vector.# Your code must work no matter how many values are in the vector.## Example 1: # > x = c("anne","bob","carla","dave","ed","fran","george","hugh","ike","jill")# YOUR CODE GOES HERE# [1] "hugh" "ike" "jill"## Example 2: # > x = seq(10,50,by=10)# YOUR CODE GOES HERE# [1] 30 40 50############################################################################.#------------.# Answer: #------------.# Example 1:x =c("anne","bob","carla","dave","ed","fran","george","hugh","ike","jill")x[ (length(x)-2):length(x) ] # ANSWER
[1] "hugh" "ike" "jill"
# Example 2: x =seq(10,50,by=10)x[ (length(x)-2):length(x) ] # ANSWER
[1] 30 40 50
#####################################################################.# Don't use c(...) when it is not necessary #########################################################################.# c() is only required to combine multiple vectors into a single vector.# Do not use c for a single vector.students =c("joe", "sue") # c is requiredc(students) # c is not required - since there is only one vector - dont use c here
[1] "joe" "sue"
students
[1] "joe" "sue"
c(seq(1,10,by=2)) # c is not required because seq is already a vector! - don't use c here
[1] 1 3 5 7 9
seq(1,10,by=2)
[1] 1 3 5 7 9
c ( rep(10,3), rep(20, 2)) # c IS required because you're combining two different vectors