##################################################################################.
##################################################################################.
##
## logical data - TRUE / FALSE ####
##
## logical operators: > < >= <= == (equal to) != (not equal to) ####
##
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##################################################################################.11 Logical vectors, relational (AKA logical) operators, ifelse
11.1 Logical value - TRUE and FALSE
# R has two "logical values", i.e. TRUE and FALSE.
#
# These values are NOT variables.
#
# They are "logical values"
#
# We will understand more about why they are special and how to use them.
# Keep reading ...
TRUE[1] TRUEFALSE[1] FALSE11.2 Relational operators ( e.g. > ) result in TRUE or FALSE
#--------------------------------------------------------------------------.
# Using logical operators ( e.g. > ) results in TRUE or FALSE ####
#--------------------------------------------------------------------------.
3 > 2 # TRUE[1] TRUE2 > 3 # FALSE[1] FALSE11.3 multiple answers for longer vectors, recycling rule
#--------------------------------------------------------------------------.
# Using logical operators ( e.g. > ) with vectors of many values results in many TRUE/FALSE values ####
#--------------------------------------------------------------------------.
c(10,20,30,40) > 25 # FALSE FALSE TRUE TRUE[1] FALSE FALSE TRUE TRUE# Values are compared position by position
c(10,20,30,40) > c(100, 1, 1, 100) # FALSE TRUE TRUE FALSE[1] FALSE TRUE TRUE FALSE# Recycling rule works
c(10,20,30,40) > c(1, 100) # TRUE FALSE TRUE FALSE[1] TRUE FALSE TRUE FALSE# original: c(10,20,30,40) > c(1, 100)
#
# recycle: c(10,20,30,40) > c(1, 100, 1, 100)
#
# > : c(10>1, 20>100, 30>1, 40>100)
#
# Final: TRUE FALSE TRUE FALSE11.4 The == and != operators
#------------------------------------------------------------.
# USE == (i.e. double == signs) to test for equality.
#
# USE != to test for "not equal to"
#------------------------------------------------------------.
# REMEMBER - test for equality uses two == signs (assignment uses one = sign)
# Use double == to test the TRUTH of an expression
10+2 == 4*3 # TRUE[1] TRUE10+2 = 4*3 # Error - single = sign is for assignment to a variable or specifying an argument valueError in 10 + 2 = 4 * 3: target of assignment expands to non-language object# Test for not-equals using !=
10+2 != 4*4 # TRUE, i.e. 10+2 is NOT EQUAL to 4*4[1] TRUE10+2 != 4*3 # FALSE[1] FALSE10+2 == 4*4 # FALSE[1] FALSE11.5 Type ?“>” to get help on relational operators
# To get help for the relational operators, type ?`>` ####
?">"starting httpd help server ... done# Relational operators (i.e. > < >= <= == !=) also use vector operations and the recycling rule. ####
c(10, 20, 30, 40) > c(5, 25, 28, 100)[1] TRUE FALSE TRUE FALSE# original : c(10, 20, 30, 40) > c(5, 25, 28, 100)
# : c(10>5 , 20>25 , 30>28 , 40>100)
# : c(TRUE , FALSE , TRUE , FALSE)
c( rep(10,4), rep(20, 4)) > c(5,25,28,100)[1] TRUE FALSE FALSE FALSE TRUE FALSE FALSE FALSE# original: c( rep(10,4), rep(20, 4)) > c(5,25,28,100)
# do the rep's: c(c(10,10,10,10), c(20,20,20,20) ) > c(5, 25, 28, 100)
# combine the c's : c( 10,10,10,10,20,20,20,20) > c(5,25,28,100)
# recycling: :c(10,10,10,10,20,20,20,20) > c(5,25,28,100,5,25,28,100)
# final answer : TRUE FALSE FALSE FALSE TRUE FALSE FALSE FALSE
# The following uses the recycling rule
c(10, 20) > c(5, 25, 30, 12)[1] TRUE FALSE FALSE TRUE# original : c(10, 20) > c(5, 25, 30, 12)
# recycling rule: c(10, 20, 10, 20) > c(5, 25, 30, 12)
# : c(10>5 , 20>25, 10>30 , 20>12)
# : c(TRUE , FALSE, FALSE, TRUE)
# You can store logical values (i.e. TRUE and FALSE) in a vector.
# A vector may only contain one "mode" or "type" of data, e.g. numeric or logical. ####
someLogicalValues = c(TRUE,FALSE, TRUE, TRUE)
someLogicalValues[1] TRUE FALSE TRUE TRUEsomeNumbers = c(100,200,300)
someNumbers[1] 100 200 300# Soon, we'll learn much more about logical values and how they
# are used in R ...11.6 — Practice
############################################################################.
# QUESTION:
#
# Write a function with the following "signature" (the signature of a
# function includes the name of the function and the names of the arguments
# for the function)
#
# isEven = function( nums )
#
# nums is expected to be a numeric vector. The function should return
# TRUE values for the even values in nums and FALSE values for the odd
# values in nums.
#
# EXAMPLE:
# > isEven( c(2,5,10,20,23) )
# [1] TRUE FALSE TRUE TRUE FALSE
#
# HINT: Even numbers have a remainder of zero when they are divided by two.
############################################################################.
# ANSWER
isEven = function( nums ){
nums %% 2 == 0
}
# Test cases:
isEven( c(2,5,10,20,23) ) # should return TRUE FALSE TRUE TRUE FALSE[1] TRUE FALSE TRUE TRUE FALSEisEven( 11 ) # should return FALSE[1] FALSEisEven( -8 ) # should return TRUE[1] TRUE11.7 ifelse( LOGICAL_VECTOR , SOME_VECTOR , ANOTHER_VECTOR )
###########################################################################.
# ifelse( LOGICAL_VECTOR , SOME_VECTOR , ANOTHER_VECTOR )
#
# NOTE: R's ifelse function, works similarly to Excel's "if" function.
# However, R's version is "vectorized" (see below for examples)
############################################################################.
?ifelse
# Example:
# In the following example we explicitly write TRUE, FALSE, TRUE just to make
# it more obvious how the ifelse function works. Obviously you would
# not write code like this.
ifelse(c(TRUE, FALSE, TRUE), c(5, 10 , 15) , c(100, 200, 300)) # 5 200 15[1] 5 200 15# Rather, the following is more like what you might see. However, this wouldn't
# appear in real code either since everyone knows that 10>2 is TRUE - why would
# we need to write that.
ifelse(c(10>2, 100>99999, 5==3+2), c(5, 10 , 15) , c(100, 200, 300)) # 5 200 15[1] 5 200 15# In "real life code" there would be variables that are part of the code (see
# examples below.)
# Display the word "even" for the even numbers and "odd" for the odd numbers:
nums = c(2, 5, 10, 21, 23, 30)
ifelse( nums %% 2 == 0,"even","odd") # "even" "odd" "even" "odd" "odd" "even"[1] "even" "odd" "even" "odd" "odd" "even"# original: ifelse( nums %% 2 == 0,"even","odd")
#
# expand logical expression: ifelse(c(TRUE FALSE TRUE FALSE FALSE TRUE), "even", "odd")
#
# recyle the "even" and "odd" values into vectors of lenghth 6 to match the lenght
# of the logical vector.
# ifelse(c(TRUE FALSE TRUE FALSE FALSE TRUE),
# c("even", "even", "even", "even", "even", "even"),
# c("odd", "odd", "odd", "odd", "odd", "odd"))
#
# result: "even" "odd" "even" "odd" "odd" "even"
# If the function isEven exists already then the above code could be
# rewriten as follows:
ifelse(isEven(nums), "even","odd") # "even" "odd" "even" "odd" "odd" "even"[1] "even" "odd" "even" "odd" "odd" "even"