1515. “character” values (also known as “strings”), cat(), nchar(), paste(), paste0()
#########################################################################.#########################################################################.## ## character values (also known as "strings")#### character values must be surrounded by## "quotes" (also known as "double quotes") or ## 'apostrophes' (also known as 'single quotes')###########################################################################.#########################################################################.# R has different types (or "modes") of data.# We've already seen numeric data and logical (TRUE/FALSE) data.# The other type (or "mode") of data we will learn about now# is "character" data.## Character data can contain ANY "characters" but the characters must# be surrounded by "double quotes" (i.e. quotes) or 'single quotes'# (i.e. apostrophes).# Character data can be used to store words greeting <-"hello"mode(greeting) # "character"
# character data MUST be surrounded by "quotes" or 'apostrophes' # (they basically do the exact same thing in R)## "quotes" are often called "double quotes" (i.e. there are 2 lines for each quote)# 'apostrophes' are often called 'single quotes' (i.e. there is 1 line for each apostrophe)rep("hello", 5) # "hello" is a character value, 5 is a numeric value
[1] "hello" "hello" "hello" "hello" "hello"
rep('hello', 5) # 'hello' is a character value, 5 is a numeric value
[1] "hello" "hello" "hello" "hello" "hello"
# If you leave off the quotes, R will assume hello is a variable namerep(hello, 5) # ERROR - variable hello doesn't exist.
Error: object 'hello' not found
15.2 R always displays character data surrounded with “double-quotes”
#------------------------------------------------------------------------------.# Even if you use 'single quotes' to create a character vector, R will display# the information with "double quotes". That is fine. Remember, 'single quotes'# and "double quotes" are basically the same to R.#------------------------------------------------------------------------------.fruit =c("apple", "banana", "pear") # "double-quotes"fruit # no surprises: "apple" "banana" "pear"
[1] "apple" "banana" "pear"
vegetables =c('potato', 'carrot') # assigned with 'single-quotes'vegetables # but displays with "double-quotes", i.e. "potato" "carrot"
[1] "potato" "carrot"
15.3 Many functions (e.g. length, rep, etc) work with all types of vectors
#-------------------------------------------------------------------.# Many functions that you already know (e.g. length, rep)# work with any type of vector (numeric, logical, character).#-------------------------------------------------------------------.people <-c("joe", "sue", "sam", "alice") # "double quotes"people
# As with numeric values, you don't need an actual variable.# You can type the character values directly in wherever you want # to use it. You can use the c() function to create a vector with # more than one value.rep(c("bob", "anne"), 2) # "bob" "anne" "bob" "anne"
[1] "bob" "anne" "bob" "anne"
15.4 Surround data containing quotes with apostrophes (and vice versa)
#-----------------------------------------------------------------------.# Mixing "double quotes" and 'single quotes'## Don't place 'apostrophes' inside of 'apostrophes' and# don't place "quotes" inside of "quotes"# unless ... (keep reading)##-----------------------------------------------------------------------.# You may type apostrophes inside of quotes (e.g. "How's it going?")# and quotes inside of apostrophes (e.g. 'He said "Hello" to Sue').saying <-c("What's up?") # apostrophe inside quotes - that's finesaying
[1] "What's up?"
sentence <-'He said "Hello" to Sue.'# "quotes" inside apostrophes is fine too# When you display information that has a "quote" inside of a character value# R will display the quotes that are inside of the value with a# backslash before the quote, i.e. \"sentence # "He said \"Hello\" to Sue."
[1] "He said \"Hello\" to Sue."
# BACKSLASH \ (used to "escape" quotes or apostrophes)# FORWARD SLASH / (used for division, e.g. 3/4)
15.5 Quoting text that contains the same type of quote leads to errors.
#----------------------------------------------------------------------.# You will get ERRORS if you you type a quote inside of quotes# or an apostrophe inside of apostrophes. R will get confused.## You can use \" or \' to place a quote inside of quotes # or an apostrophe inside of apostrophes#----------------------------------------------------------------------.# The next line would cause an error since the entire value# is surrounded by apostrophes and it also contains an apostrophe# in the actual text (i.e. in the word How's).# (See below for an explanation of why this causes an error.)question <-c('How's it going?') # ERROR
Error in parse(text = input): <text>:14:20: unexpected symbol
13:
14: question <- c('How's
^
# How does R interpret this line of code?# # Step 1: R correctly interprets the 1st apostrophe (i.e. 'How ...)# as the start of the quoted text.## Step 2: R interprets the 2nd apostrophe (ie. the apostrophe that# appears after 'How') as the end of the quoted text.## Step 3: When R sees the 2nd apostrophe it assumes that the quotation# is over and expects to see a closing parentheses. However, instead# of a closing parentheses, the next symbol after the apostrophe# is the letter s. Therefore R gets confused and reports and error.
15.6 Use ” inside double-quotes. Use ’ inside single-quotes.
# FIX 1 - surround with "double quotes"question <-c("How's it going?") # this is finequestion
[1] "How's it going?"
# FIX 2 - use \' inside the character valuequestion <-c('How\'s it going?') # backslash-apostrophe also worksquestion # "How's it going?" (this is how it is displayed)
[1] "How's it going?"
15.7 Backslash (\) vs Forward Slash (/)
# NOTE:# There are two different slashes on most keyboards. ## BACKSLASH, "\", IS THE CORRECT SLASH:# The "backslash" i.e. "\" slants from the top left and towards the lower right.# This is the slash to use in this situation.## FORWARD SLASH, "/", IS THE WRONG SLASH:# The "forward slash" i.e. "/" slants from the lower left towards the top right.# This is NOT the slash to use in this case. This slash is used for division.## MNEMONIC TO REMEMBER \BACKSLASH vs /FORWARD SLASH# Imagine that someone is walking along next to the text from left to right.# Think of the slash as that person.# The backslash, i.e. \ , can be viewed as the person falling backwards.# The forward slash, i.e. / , can be viewed as the person falling forwards.#
15.8 Similarly, don’t type a double-quote inside of double-quotes.
# Don't place quotes inside of quotes.## ERROR: (uncomment the next line to see that it is an error)sentence <-c("Joe said "Hello" to Sue.") # ERROR - "quote" inside "quotes"
Error in parse(text = input): <text>:5:26: unexpected symbol
4:
5: sentence <- c("Joe said "Hello
^
# FIX 1 - surround the entire value with apostrophes (AKA 'single quotes')sentence <-c('Joe said "Hello" to Sue.') # this works# NOTE: When you display a character value that contains quotation marks, R# puts a backslash (\) in front of the quotation mark that is inside the quote.# We'll explain more about this below.sentence # "Joe said \"Hello\" to Sue." (this is how it is displayed)
[1] "Joe said \"Hello\" to Sue."
# FIX 2 - use \" inside the character valuesentence <-c("Joe said \"Hello\" to Sue.")sentence
[1] "Joe said \"Hello\" to Sue."
# The backslashes demonstrate that the quotes with the backslashes are# inside of the character value and do not surround (i.e. delimit) the# character value.sentence # "Joe said \"Hello\" to Sue."
[1] "Joe said \"Hello\" to Sue."
# You can use the cat function to display the sentence in a more readable# way. The output of cat doesn't display any quotes # around the sentence. cat also doesn't display the backslashes (\) that# precede the quotes inside the sentence. In short, cat is used to # display the information in a "human friendly" way.# We will discuss the cat function in more depth below. However, for now# you can use cat to display the text in a more readable manner. cat(sentence) # Joe said "Hello" to Sue
Joe said "Hello" to Sue.
15.9 MIXING ‘single quotes’ and “double quotes” in the same text.
#-----------------------------------------------------------------.# MIXING 'single quotes' and "double quotes" in the same text.#-----------------------------------------------------------------.# If your data contains both quotation marks and apostrophes, you # should surround your data with either type of quote and then # use backslashes in front of that type of quote in your data.# # The following are all valid and all result in the same thing.# . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .# One way - surround with "double quotes" (i.e. quotation marks), use \" in the data# . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .saying ="He's going to ask Sue \"Will you marry me\". He hopes she says yes."saying # this is what is stored
[1] "He's going to ask Sue \"Will you marry me\". He hopes she says yes."
cat(saying) # this is a "human friendly" view of your data
He's going to ask Sue "Will you marry me". He hopes she says yes.
# . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .# Another way - surround with 'single quotes' (i.e. apostrophes), use \' in the data# . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .saying ='He\'s going to ask Sue "Will you marry me". He hopes she says yes.'saying # this is what is stored
[1] "He's going to ask Sue \"Will you marry me\". He hopes she says yes."
cat(saying) # this is a "human friendly" view of your data
He's going to ask Sue "Will you marry me". He hopes she says yes.
# . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .# Yet another way - the backslashes are ok, even if they aren't necessary# . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .# The following uses \' and \" in the data. # You don't need \" since the data is surrounded with 'single quotes'.# The \" is unnecessary in this case but it doesn't hurt.saying ='He\'s going to ask Sue \"Will you marry me\". He hopes she says yes.'saying # this is what is stored
[1] "He's going to ask Sue \"Will you marry me\". He hopes she says yes."
cat(saying) # this is a "human friendly" view of your data
He's going to ask Sue "Will you marry me". He hopes she says yes.
15.10 cat(value1, value2, etc.)
###########################################################################.# cat( value1, value2, etc. )## WHAT DOES IT DO## The cat function is used to display information to the screen in a # user friendly way. The output of cat will NOT include extra backslash characters.# The output of cat will also not be surrounded with quotes.### YOU CANNOT "USE" THE OUTPUT OF CAT (other than to display information)## The output of cat iS ONLY used to display information to the screen.# You cannot capture the output of cat to a variable or use cat in a# larger expression. It is simply used to display information to the screen.# See below for an example of what happens if you try to use the output # from cat in a larger context (hint ... it doesn't work).### SOME TRIVIA - WHY IS IT CALLED CAT? ## If you're wondering why it's called "cat", it is because "cat" is short for# the English word "concatenate". "concatenate" means to "link things together"# - https://www.dictionary.com/browse/concatenate . The cat function can take# multiple pieces of info and display them all together to the screen (see # the example code below). Incidentally, the "c()" function is also short # for "concatenate" since it "concatenates" (or combines) multiple different# vectors into a single combined vector.## The command "cat" predated the creation of R. It originated with the# Unix operating system in the 1970's and was carried over to the Linux# operating system which is very popular today. As often happens with# programming languages and technology, newer languages and technology (e.g. R)# inherit many of the features (i.e. cat) that were present in older# languages and technology (e.g. Unix). ###########################################################################.#----------------------------------------------------------------.# cat displays values to the screen in a "human friendly" way.#----------------------------------------------------------------.# Set a character value ...sentence <-"Joe said \"Hello\" to Sue."# Display the results ...## To see the actual character value without the backslashes, you can use the cat function.# Compare the difference in output of the following two lines.# Notice that for cat there are no quotes around the text and no backslashes within the text.sentence # "Joe said \"Hello\" to Sue."
[1] "Joe said \"Hello\" to Sue."
cat(sentence) # Joe said "Hello" to Sue. (no backslashes, no "quotes" surrounding the data)
Joe said "Hello" to Sue.
# You can use cat to output multiple pieces of information to the screen.# This includes multiple values within a single vector as well as # multiple different vectors.# By default all items are separated with spaces.people =c("joe", "sue", "bill")food =c("apple", "orange", "pear")cat(people, food) # just outputs all values
joe sue bill apple orange pear
# You can change the separator to anything you like by using the sep argumentcat (people, food, sep="-")
joe-sue-bill-apple-orange-pear
cat (people, food, sep=":---:") # the separator can be anything, even multiple characters
cat (people, food, sep="") # use the "" empty string to remove the separator
joesuebillappleorangepear
# another exampletf =TRUEgrade =100person ="Bill"cat ( "It is", tf, "that", person, "got", grade, "on the test!")
It is TRUE that Bill got 100 on the test!
15.11 WILF - UP TO HERE - AFTER CLASS 9
15.12 \n \t \\
#########################################################.# The backslash \ #########################################################.# The backslash character ( \ ) is used to change the meaning from # the character that follows it. When used before a "double quote" (i.e. \" ) or# a 'single quote' (i.e. \' ) it takes the special meaning of the quote away.# The quote is no longer used to indicate the end of a quotation but becomes intead# simply part of the text.# # In a similar way, the backslash changes the meaning of some other characters.# For example# \n is used for an ENTER (i.e. a "newline").# \t is used for a "tab" character# \\ is used for an actual backslash character.## EXAMPLEcat("This is line 1.\nThis is line 2.") # displayed on two different lines
This is line 1.
This is line 2.
cat("This is line 1.\n\nWe just skipped a line.") # use double \n\n to skip a line
This is line 1.
We just skipped a line.
cat("Hi.\tI really like pizza.\n\tI don't like broccoli.") # two lines, notice the tabs
Hi. I really like pizza.
I don't like broccoli.
cat("This ... \\ ... is a backslash.")
This ... \ ... is a backslash.
15.13 — Practice —
#...........................................................................# QUESTION TOPICS: cat, backslash## (a) Write a single R command that assigns the following message# to the variable named message.# # The '\' is known as a "backslash". # It's used to escape the meaning of# the character that follows it.## (b) display the message variable to the screen by just typing the word, message.# (c) Use the cat command to display the message to the screen.#...........................................................................
click here for answer
message ="\tThe '\\' is known as a \"backslash\".\n\tIt's used to escape the meaning of\n\tthe character that follows it."message # this shows the backslashes, ie. \n \t \" \'
[1] "\tThe '\\' is known as a \"backslash\".\n\tIt's used to escape the meaning of\n\tthe character that follows it."
cat(message) # this changes \n into ENTER, \t into tab, \" into " and \' into '
The '\' is known as a "backslash".
It's used to escape the meaning of
the character that follows it.
15.14 DON’T use cat inside a larger expression.
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~# Do NOT use the output of cat inside a larger expression. ##### (you CAN use the output of most other functions in a larger expression)# # See examples below#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#-----------------------------------------------.# SETUP SOME DATA TO USE IN THE EXAMPLES BELOW#-----------------------------------------------.# people and food are parallel vectors # - i.e. joe's favorite food is apple, sue's favorite food is orange, etc.people =c("joe", "sue", "bill") favoriteFood =c("apple", "orange", "pear")people[2] # use the number 2 to get the 2nd person
[1] "sue"
cat(2) # this just uses cat to display the number 2 on the screen
2
# . . . .. . . . . . . . . . . . . . . . . . . . . .. . . # ONLY USE cat TO DISPLAY INFO TO THE SCREEN.# DON'T USE CAT FOR ANYTHING ELSE!# . . . .. . . . . . . . . . . . . . . . . . . . . .. . . #...........# EXAMPLE 1#...........# ONLY USE cat TO DISPLAY INFO TO THE SCREEN.# DON'T USE CAT FOR ANYTHING ELSE - THIS DOESN'T WORKpeople[cat(2)] # error
2
character(0)
# HOWEVER, THIS WORKS - use an expression to display the 2nd personpeople[ 1+1 ] # sue
[1] "sue"
#...........# EXAMPLE 2#...........# ONLY USE cat TO DISPLAY INFO TO THE SCREEN.# DON'T USE CAT FOR ANYTHING ELSE - THIS DOESN'T WORKy =cat(people[3]) # "bill"
bill
y # NULL
NULL
# Set the variable x to the name of the 2nd personx = people[2] # this worksx
[1] "sue"
15.15 nchar returns the number of symbols (letters, digits, spaces, etc) in a value.
########################################################.# a few character functions : nchar, paste0, paste # (there are many more): ########################################################.#---------------------------------------------------------.# nchar returns the number of characters in a value.# All characters, including spaces and punctuation count as part of the value.#---------------------------------------------------------.nchar(c("O.K.", "hello", "there", "hello there"))
[1] 4 5 5 11
wierdGreeting ="hello\n\tthere"cat(wierdGreeting)
hello
there
nchar(wierdGreeting)
[1] 12
15.16 paste and paste0 combine character values from different vectors
#-------------------------------------------------------------------.# paste and paste0 functions are used to combine character values#-------------------------------------------------------------------.paste0 ( "hi", "there") # paste0 does not leave any space between values
[1] "hithere"
# You can capture the output of these functions in a variablegreeting =paste0("hi", "there", "joe")greeting
[1] "hitherejoe"
nchar(greeting)
[1] 10
# paste (as opposed to paste0)paste("hi", "there")
[1] "hi there"
paste("hi", "there", "joe") # paste by default leaves a space
[1] "hi there joe"
# you can change the separator with a sep argument paste("hi", "there", "joe", sep ="-")
# the empty string is "" or ''paste("hi", "there", "joe", sep ="") # exact same thing as paste0
[1] "hitherejoe"
# Like most functions, paste0 and paste work with the recycling rulefirstNames =c("joe","chaim","juan")firstNames
[1] "joe" "chaim" "juan"
paste ("hello", firstNames)
[1] "hello joe" "hello chaim" "hello juan"
paste0 ("hello", firstNames)
[1] "hellojoe" "hellochaim" "hellojuan"
# becomes paste0( c("hello","hello","hello"), c("joe","chaim","juan"))# vector operations "hellojoe" "hellochaim" "hellojuan"#...........................................................# Using paste with vectors that have more than one value#...........................................................firstNames =c("joe","chaim","juan")firstNames
[1] "a x somethingElse" "b y somethingElse" "a z somethingElse"
#.....................................................................# collapse argument is used to collapse entire output into a # vector that contains a single item## The value of the collapse argument is used to separate between the different# values that are being collapsed.#.....................................................................# example of using collapsepaste(c("abc","def"), c("RST", "UVW","XYZ"), sep="") # without collapse
[1] "abcRST" "defUVW" "abcXYZ"
paste(c("abc","def"), c("RST", "UVW","XYZ"), sep="", collapse="-") # with collapse
[1] "abcRST-defUVW-abcXYZ"
# another exampleanswer =paste(firstNames, lastNames, sep="---") # without collapse answer
# student's questionpaste(firstNames, lastNames, sep=" ", collapse="") # sep is space
[1] "joe smithchaim schwartzjuan rodriguez"
paste(firstNames, lastNames, collapse="") # same thing (default for sep is a space)
[1] "joe smithchaim schwartzjuan rodriguez"
15.17 Can’t do math with “character” values: “1” + “1” = ERROR
#---------------------------------------------------------------------------.# You cannot do math with character data - even if it looks like a number#---------------------------------------------------------------------------."5"*"3"# ERROR
Error in "5" * "3": non-numeric argument to binary operator
#----------------------------------------------------------------------------.# sorting character data## In general, sort will arrange character data in alphabetical order.## The sort order of "special characters" (@%#$ etc) spaces, numbers,# CAPITALS vs lowercase depends on the "locale" of your computer,# e.g. USA, Europe, Israel, etc.# Discussion of "locale" is beyond the scope of this document. #----------------------------------------------------------------------------.stuff =c("table", "@table", " table", "book case", "101 dalmations", "apple", "ape", "apex")stuff
#.................................................................................# If numbers are stored as characters then they will sort as characters do.## The first character is the most important character for the sorting order. # Only when two of the first characters are the same will the 2nd character be important, etc.#.................................................................................sort(charNums) # "099" "100" "1000000" "103" "19" "2000" "22" "85" "9"
# EXPLANATION OF THE SORT ORDER## "099" sorts first because 0 is the "earliest" character in the # sequence 0,1,2,3,4,5,6,7,8,9## 100 is next because "1" is after "0" in the sequence 01,2,3,4,5,6,7,8,9## 1000000 is next because the first 3 characters, i.e. "100" is the same# as the previous value, i.e."100" but "1000000" is longer than "100" in characters# so it sorts after "100". This is similar to why "be" is followed by "bed" in the dictionary# "bed" contains "be" but is longer than "be".## "103" is next because the "10" is the same as the first two characters of the # previous value but the third character, i.e. "3" is "later" in the list 0,1,2,3,4,5,6,7,8,9# than is "0", the third character of "1000000".## "19" is next because "9" is later than the "0" from "103"## "2000" is next because the "2" is later than the "1" from "19"## "22" is next because the 2nd "2" is later then the first "0" from "2000"## "85" is next because the "8" is later than the first "2" from "22"## "9" is last because it has the latest first character from the list 01,2,3,4,5,6,7,8,9 from# all of the values being sorted.
15.22 Some functions automatically convert “1” to 1
##############################################################.# Sometimes, R implicitly (i.e. automatically) converts# character values into numeric values. See one example# shown below with the rep function.##############################################################.# The rep function expects a numeric value as its second argument.rep("hello", 5) # "hello" is character, 5 is numeric
[1] "hello" "hello" "hello" "hello" "hello"
# If instead you specify a character value that contains a # number, the rep function will convert the character into a # number.rep("hello", "5") # "5" is converted to 5
[1] "hello" "hello" "hello" "hello" "hello"
# However such conversions are NOT guaranteed to happen for all functions.# For example, the 2nd argument to the round function is used to specify # to what position to round the number. For example the following line# rounds 3.579 to the 1st decimal placeround(3.579, 1) # 3.6
[1] 3.6
# If you specify the character value "1" for the 2nd argument # instead of the number 1 you will get an ERROR since the 2nd argument# is supposed to be numeric.round(3.579, "1") # ERROR - "1" is a character value, should be a number
Error in round(3.579, "1"): non-numeric argument to mathematical function
# Bottom line - the functions that are built into R are not consistent# in how they handle this issue.