R learning by examples

R data structures
VECTOR
[1]

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MATRIX
[2]

[3]

1 row, N columns.
One data type only (numeric, character, date, OR logical).
Uses: track changes in a single variable over time.
Examples: stock prices, hurricane path, temp readings, disease spread,
financial performance, sports scores.

[,1]

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•
•

[,3]

[1,]
[2,]
[3,]
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•
•

N row, N columns.
One data type only (any combination of numeric, character, date, logical).
Basically, a collection of vectors.

DATA FRAME

LIST
[1]

[,2]

[2]

[,1]

[3]

1 row, N columns. Multiple data types.
Uses: ist detailed information for a person/place/thing/concept.
Examples: Listing for real estate, book, movie, contact, country, stock,
company, etc. Or, a "snapshot" or observation of an event or phenomenon
such as stock market, or scientific experiment.

[,2]

[,3]

[1,]
[2,]
[3,]
•
•
•

N rows, N columns.
Multiple data types.
Basically, a collection of lists or snapshots which when assembled together
provide a "bigger picture."

Other important R concepts
FACTORS

USER-DEFINED FUNCTIONS

Stores each distinct value only once, and the data itself is stored as a vector of
integers. When a factor is first created, all of its levels are stored along with the
factor.

> f <- function(a) { a^2 }
> f(2)
[1] 4

> weekdays=c("Monday","Tuesday","Wednesday","Thursday","Friday")
> wf <- factor(weekdays)
[1] Monday
Tuesday
Wednesday Thursday Friday
Levels: Friday Monday Thursday Tuesday Wednesday

Used to group and summarize data:
WeekDaySales <- (DailySalesVector, wf, sum)
# Sum daily sales figures by M,T,W,Th,F

PACKAGES, FUNCTIONS, DATASETS
> search() # Search for installed packages & datasets
[1] ".GlobalEnv"
"mtcars"
"tools:rstudio"
[4] "package:stats"
"package:graphics" "package:grDevices"

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•
•
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SPECIAL VALUES
•
•
•

# List available datasets

pi=3.141593. Use lowercase "pi"; "Pi" or "PI" won't work
inf=1/0 (Infinity)
NA=Not Available. A logical constant of length 1 that means neither
TRUE nor FALSE. Causes functions to barf.
•
Tell function to ignore NAs: function(args, na.rm=TRUE)
•
Check for NA values: is.na(x)

> library(ggplot2) # load package ggplot2
Attaching package: ‘ggplot2’
> data()

Functions can be passed as arguments to other functions.
Function behavior is defined inside the curly brackets { }.
Functions can be nested, so that you can define a function inside another.
The return value of a function is the last expression evaluated.

•

NULL=Empty Value. Not allowed in vectors or matrixes.
•

> attach(iris) # Attach dataset "iris"

•

Check for NULL values: is.null(x)

NaN=Not a Number. Numeric data type value for undefined (e.g., 0/0).

See this for NA vs. NULL explanation.

VECTOR:
Examples

[1]

[2]

[3]

VECTORS

[1]

[2]

[3]

# 1xN array of same data type
> v<-c(1:3); v
[1] 1 2 3
> mode(v)
# displays data type
[1] "numeric"
> v <-c("one", "two", "three"); v
[1] "one"
"two"
"three"
> mode(v)
[1] "character"
> v <-c(TRUE,FALSE,TRUE); v
[1] TRUE FALSE TRUE
> mode(v)
[1] "logical"
> v<-c(pi, 2*pi, 3*pi); v
[1] 3.141593 6.283185 9.424778
> mode(v)
[1] "numeric"
# Numeric values coerced into character mode
> v<-c(1,2,3,"one", "two", "three"); v
[1] "1"
"2"
"3"
"one"
"two"
"three"
> mode(v)
[1] "character"

BASIC OPERATIONS
# Addition
> v1<-1:3
> v2 <- c(10,10,10)
> mode(v1)
[1] "numeric"
> mode(v2)
[1] "numeric"
> v1+v2
[1] 11 12 13
# Multiplication &
Division
> v1 * v2
[1] 10 20 30
> v1 / v2
[1] 0.1 0.2 0.3
> v2 / v1
[1] 10.000000 5.000000
3.333333

#Subtraction
> v1-v2
[1] -9 -8 -7
> v2-v1
[1] 9 8 7
# Logical Comparison
> v1==v2
[1] FALSE FALSE FALSE
> v1 != v2
[1] TRUE TRUE TRUE
> v1 > v2
[1] FALSE FALSE FALSE
> v1 < v2
[1] TRUE TRUE TRUE

VECTORS

[1]

[2]

[3]

# By default, column numbers are used as indexes
> v3[1]
[1] 1
# But columns can be given meaningful names…
> names(v3) # What are current column names?
NULL
> names(v3)<- c("1st","2nd","3rd","4th","5th",
"6th") # Rename column names.
> names(v3) [1] "1st" "2nd" "3rd" "4th" "5th"
"6th"
> v3
1st 2nd 3rd 4th 5th 6th
1
2
3 10 10 10
# Now we can use names as indexes:
> v3["6th"] # same as v3[6]
6th
10
> v3[c("1st","6th")] # same as v3[c(1,6)]
1st 6th
1 10
> v3[-1] # Can exclude columns using (-)
2nd 3rd 4th 5th 6th
2
3 10 10 10

INDEXING, SELECTING
& SUBSETTING
> v3[v3==10] # Select values equal to 10
[1] 10 10 10
> v3[v3!=10] # Select values NOT equal to 10
[1] 1 2 3
> median(v3)
[1] 6.5
> v3[v3<median(v3)] # Select values < median
[1] 1 2 3
> v3[v3>median(v3)] # Select values > median
[1] 10 10 10
> v3 < median(v3) # Test if value < median?
[1] TRUE TRUE TRUE FALSE FALSE FALSE
> v3 %% 2==0 # Test if value is an even number?
[1] FALSE TRUE FALSE TRUE TRUE TRUE
> v3 %% 2==1 # Test if value is an odd number?
[1] TRUE FALSE TRUE FALSE FALSE FALSE

LIST:
Examples

[1]

[2]

Product Details









Series: O'Reilly Cookbooks
Paperback: 438 pages
Publisher: O'Reilly Media; 1 edition (March 22, 2011)
Language: English
ISBN-10: 0596809158
ISBN-13: 978-0596809157
Product Dimensions: 0.9 x 7 x 9.2 inches
Shipping Weight: 1.6 pounds

[3]

LISTS

[[1]]

[[2]]

[[3]]

# 1xN array of multiple data types/modes
> c1 <-c("A", "B", "C")
> n1 <-c(1:3)
> l2 <- list(c1,n1,Sys.Date(),TRUE);l2
[[1]]
[1] "A" "B" "C"
[[2]]
[1] 1 2 3
[[3]]
[1] "2013-11-03"
[[4]]
[1] TRUE
> str(l2)
List of 4
$ : chr [1:3] "A" "B" "C"
$ : int [1:3] 1 2 3
$ : Date[1:1], format: "2013-11-03"
$ : logi TRUE
> l2[[4]]
[1] TRUE
> l2[[1]]
[1] "A" "B" "C"
------->fix('l2')
list(c("A", "B", "C"), 1:3, structure(16012, class =
"Date"),TRUE)

# Append to a list; the results get trippy
> l2 <- list(l2,pi); l2
[[1]]
[[1]][[1]]
[1] "A" "B" "C"
[[1]][[2]]
[1] 1 2 3
[[1]][[3]]
[1] "2013-11-03"
[[1]][[4]]
[1] TRUE
[[2]]
[1] 3.141593

# Basically, a new () gets added each time the list is
appended
list(list(c("A", "B", "C"), 1:3, structure(16012, class =
"Date"), TRUE), 3.14159265358979)
# [[1]] is not the same as [1]
> mode(l3[[1]])
[1] "numeric"
> mode(l3[1])
[1] "list"
# To avoid confusion, use names
> l3 = list(x=1,y=2,z=3); l3
$x
[1] 1
$y
[1] 2
$z
[1] 3
> l3$x # this is the same as l3[[1]]
[1] 1

MATRIX:
Examples

[,1]
[1,]
[2,]
[3,]

[,2]

[,3]

Recommendation
Engine
Matrices

bought bought bought

bought likely buy likely buy

DATA FRAME:
Examples

[,1]

[,2]

[,3]

[1,]
[2,]
[3,]

Data Frames: Most frequently used structure for storing and manipulating
data sets. Similar to:
• A database table
• A spreadsheet
Like the above, DFs have rows x columns, but terminology is different:
• Observations = rows
• Variables = Columns
R Table vs. Data Frame: KISS and stick to data frames for now.
#Convert table to data frame:
> HEC <- data.frame(HairEyeColor)
> str(HEC)
'data.frame':32 obs. of 4 variables:
$ Hair: Factor w/ 4 levels "Black","Brown",..: 1 2 3 4 1 2 3 4 1 2 ...
$ Eye : Factor w/ 4 levels "Brown","Blue",..: 1 1 1 1 2 2 2 2 3 3 ...
$ Sex : Factor w/ 2 levels "Male","Female": 1 1 1 1 1 1 1 1 1 1 ...
$ Freq: num 32 53 10 3 11 50 10 30 10 25 ...

DATA FRAMES

[,1]

[,2]

[,3]

[1,]
[2,]
[3,]

# HEC[1,] returns a row
> HEC[1,]
Hair
Eye Sex Freq
1 Black Brown Male
32

# Subsetting made easier
> HEC6 <-subset(HEC,select=Hair); str(HEC6)
'data.frame':
32 obs. of 1 variable:
$ Hair: Factor w/ 4 levels "Black","Brown",..: 1 2 3 4
> HEC7 <-subset(HEC,select= c(Hair,Eye)); str(HEC7)
'data.frame':
32 obs. of 2 variables:
$ Hair: Factor w/ 4 levels "Black","Brown"...
$ Eye : Factor w/ 4 levels "Brown","Blue"...
> HEC8 <-subset(HEC, subset=(Hair == "Black" & Eye ==
"Brown")); HEC8
Hair
Eye
Sex Freq
1 Black Brown
Male
32
17 Black Brown Female
36

INDEXING, SELECTING
& SUBSETTING
# HEC[[1]], HEC[,"Hair"], HEC$Hair return column
> HEC1 <-HEC[[1]]; HEC1
> str(HEC1)
Factor w/ 4 levels "Black","Brown",..: 1 2 3 4 1 2 3 4 1 2 ...

# HEC[1] and HEC["Hair"] return column dframe
> HEC2 <-HEC[1]; HEC2
> str(HEC2)
'data.frame':32 obs. of 1 variable:
$ Hair: Factor w/ 4 levels "Black","Brown",..: 1 2 3 4 1 2 3 4 1 2

> HEC4 <-HEC["Hair"]
> HEC2 == HEC4
Hair
[1,] TRUE
[2,] TRUE

#
#
>
>

etc.

Returning multiple columns in a data frame
This is the same as HEC[,c(1, 4)]
HEC5 <-HEC[,c("Hair", "Freq")]
str(HEC5)

'data.frame':
32 obs. of 2 variables:
$ Hair: Factor w/ 4 levels "Black","Brown",..: 1 2 3 4 1 2 3 4 1
$ Freq: num 32 53 10 3 11 50 10 30 10 25 ...

DATA FRAMES
# Combine 2 DFs columnwise

> echo <- cbind(HEC2, HEC4)
> echo
Hair Hair
1 Black Black
2 Brown Brown
3 Red
Red etc

# Stack 2 DFs (UNION)

> rbind(HEC8, HEC8)
1
17
11
171

Hair
Black
Black
Black
Black

Eye
Sex Freq
Brown
Male
32
Brown Female
36
Brown
Male
32
Brown Female
36

# Skip having to specify the DF for col names
> f <- sum(HEC$Freq)

# Instead of this

> attach(HEC)
> f <- sum(Freq) # Use this

FUNCTIONS
SEQUENCING
seq(from,to,by) generate a sequence

indices <- seq(1,10,2)
#indices is c(1, 3, 5, 7, 9)

rep(x,ntimes)

repeat x n times
y <- rep(1:3, 2)
# y is c(1, 2, 3, 1, 2, 3)

cut(x,n)

divide continuous variable in factor
with n levels
y <- cut(x, 5)

DATE PROCESSING
Sys.Date()

as.date()

generate today's date
> Sys.Date()
[1] "2013-11-03

Convert string to date format
> to=as.Date('2006-1-10')
> mode(to)
[1] "numeric"
> class(to)
[1] "Date"

CHARACTER PROCESSING Description
substr(x, start=n1, stop=n2)

Extract or replace substrings in a character vector.
x <- "abcdef"
substr(x, 2, 4) is "bcd"
substr(x, 2, 4) <- "22222" is "a222ef"
grep(pattern, x ,
Search for pattern in x. If fixed =FALSE then pattern is
ignore.case=FALSE, fixed=FALSE) a regular expression. If fixed=TRUE then pattern is a
text string. Returns matching indices.
grep("A", c("b","A","c"), fixed=TRUE) returns 2
sub(pattern, replacement,x,
Find pattern in x and replace with replacement text. If
ignore.case =FALSE, fixed=FALSE) fixed=FALSE then pattern is a regular expression.
If fixed = T then pattern is a text string.
sub("s",".","Hello There") returns "Hello.There"
strsplit(x, split)
Split the elements of character vector x at split.
strsplit("abc", "") returns 3 element vector "a","b","c"
paste(..., sep="")
Concatenate strings after using sep string to seperate
them.
paste("x",1:3,sep="") returns c("x1","x2" "x3")
paste("x",1:3,sep="M") returns c("xM1","xM2" "xM3")
paste("Today is", date())
toupper(x)
Uppercase
tolower(x)
Lowercase

TYPE CONVERSION

STRUCTURE CONVERSION

as.character(x)
as.complex(x)
as.numeric(x)
as.logical(x)

as.data.frame(x)
as.list(x)
as.matrix(x)
as.vector(x)

DATA TRANSFORMATIONS
VECTOR
[1]

[2]

[3]

MATRIX

# s=simplify into a vector
# sapply returns a vector
l <- sapply(lst,function)
# lapply returns a list
v <- lapply(lst,function)

[,1]

[,3]

[1,]
[2,]
[3,]

DATA FRAME

LIST
[1]

[,2]

[2]

[,1]

[3]

[1,]
[2,]
[3,]

[,2]

[,3]

GET HELPFUL INFO

PRINTING

# Get help
>help.search("cat") # find info about "cat"
>?mean # get help about function
>example(mean) # get examples

> print(matrix(c(1234),2,2))
[,1] [,2]
[1,] 1234 1234
[2,] 1234 1234

# List objects in workspace
> ls()
[1] "tbl"
"w_day"

> print(matrix(c(1,2,3,4),2,2))
[,1] [,2]
[1,]
1
3
[2,]
2
4

# List all available datasets
> data()

# Get structure
> str(HairEyeColor)
table [1:4, 1:4, 1:2] 32 53 10 3 11 50 10 30 10 25
...
- attr(*, "dimnames")=List of 3
..$ Hair: chr [1:4] "Black" "Brown" "Red" "Blond"
..$ Eye : chr [1:4] "Brown" "Blue" "Hazel" "Green"
..$ Sex : chr [1:2] "Male" "Female"
# Get Class (vector,list, dataframe, table, matrix,
numeric, function, factor,, et)
> class(HairEyeColor)
[1] "table"
# Use Google R style sheet

> print ("print works on only");print("one
string or variable at a time"); print(pi)
[1] "print works on only"
[1] "one string or variable at a time"
[1] 3.141593
> num <-1:10
> print(num)
[1] 1 2 3

4

5

6

7

8

9 10

# cat works only on strings and vectors
> cat("the first 10 numbers are:", num, "n")
the first 10 numbers are: 1 2 3 4 5 6 7 8 9 10

INPUT / OUTPUT
Ctrl-R executes the selected line(s)
# Getting and setting the working directory
> getwd()
[1] "C:/Users/mdarling/Documents"
> setwd("DA/data")
[1] "C:/Users/mdarling/Documents/DA/data"

# Enter data using spreadsheet editor
w_day <- data.frame()
w_day <- edit(w_day)
# Read data from URL
> tbl <read.csv("http://www.andrewpatton.com/countrylist.csv")

# Write data to csv file
> write.csv(tbl, "countries.csv")
#
>
>
>

Read data from HTML tables
library(XML)
url <-"http://www.andrewpatton.com/countrylist.html"
tbls <- readHTMLTable(url)

MORE DATE PROCESSING
library(timeDate)
ymdhs <- "2012-03-04 05:06:07"
pd.sec <- as.POSIXlt(ymdhs)$sec
pd.hour <- as.POSIXlt(ymdhs)$hour
pd.min <- as.POSIXlt(ymdhs)$min
pd.mday <- as.POSIXlt(ymdhs)$mday
pd.mon <- ((as.POSIXlt(ymdhs)$mon)+1)
pd.year <- ((as.POSIXlt(ymdhs)$year) + 1900)

PLOTTING
Plotting in R
- base
- ggplot2, ggmap, map
Types of Graphs
- chloropleth
- heat map
# Base plots
plot(faithful, type = 'l') #line graph
plot(faithful, type = 'p') #point graph
hist(faithful$waiting)
#histogram of column waiting
# Quickly plot a matrix of scatterplots
# This plots each column vs. all the other ones
names(iris)
[1] "Sepal.Length" "Sepal.Width" "Petal.Length"
"Petal.Width" "Species"
pairs(iris[,-5])
pairs(iris[,1:2])
# Plot x vs. y using 2 df columnns and geom_point()
ggplot(movies, aes(x=year, y=budget)) + geom_point()
# Plot histogram using 1 column, Note: geom_bar()
ggplot(movies, aes(x=year)) + geom_bar()
# plot all rows vs. mpaa column
plot(movies[, "mpaa"]) # plot has lots of nulls
mpaa.movies <- subset(movies, mpaa != "")! # exclude nulls
plot(mpaa.movies[, "mpaa"])
# Or use na.rm

R learning by examples

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