Week 1 Flashcards
library()
- List of all packages installed on your computer
- displayed in R editor
search()
List of all packages currently active on your computer
install.packages(“< lib_name >”)
- package is downloaded from CRAN and installed on your computer
- also in Tools Menu (RStudio)
library(“< lib_name >”)
- loads the library
- used after install.packages(_)
library(help = “< lib_name >”)
package documentation listed in editor
update.packages ()
- updates all packages
- also in Tools Menu (RStudio)
detach(“ package:< lib_name> “, unload=TRUE)
- Package is removed
- Package can also be removed from the right hand side window
Task
Clear the console
- Edit -> Clear Console
- Ctrl + L
comments
- start with #
- single lines only
run single command from script
- Ctrl + Enter
index number
- first number displayed in [ ]
- indexes start at 1
print(“string”)
- prints string and quotes
assignment operator
- <-
- can also use =
display variable value
type variable name in editor and execute
concatenate vectors
c(x,y) = x values, y values
multiple vectors subtraction
performs operation on values of same index
- x <- 5,5,5
- y <- 1,2,3
- x - y = 4,3,2
vector multiplication
y * 3 = each value in y vector x 3
table commands
dim(table_name)
- gives dimensions of table
- rows then columns
summary(table_name)
- gives summary stats for each column
- min, 1st quart, median, mean, 3rd, quart, max
head(table_name)
prints first 6 rows of table
names(table_name)
prints column headers / names
table( table_name $ column_name )
- makes a new table with the counts for each value type (new headers) in specified column
- eg. table(iris$species) = setosa 50 versicolor 50 virginica 50
pie(table(table name $ table column)
- creates pie chart for counts of each value in specified table column
pie(table(iris$Species ), col= purple”,”red”,”green”
assigns pie chart colors to each iris species in same order species are listed
variable names
rules
- case-sensitive
- can’t begin with number or symbol
- no blank spaces
- can use period (eg. abc.x)
vector creation
methods (3)
- Concatenate (c)
- Sequence (seq)
- Repeat (rep)
vector creation
concatenate
- c( )
- eg. y <- c(2,3,5,6)
- x <- c(first = “alpha”, second=”beta”, third=”gamma”)
concatenate
order of restriction for conversion
(Least to most restrictive)
- Strings
- Numerics
- True/False
repeat function
rep(…)
used to create vector with repeating pattern
- v = c(11,22,33)
- x = rep(v,3)
11 22 33 11 22 33 11 22 33 - gender = c(“male”,”female”)
- y = rep(gender,c(2,5))
“male” “male” “female” “female” “female” “female” “female”
vector value assignment
assigning nonexistent value to vector, matrix, array, or list expands structure to accomodate new value
- x < c(8,6,4)
- x[7] < 10
- x = 8 6 4 NA NA NA 10
repeat function
array declaration
- n <- 10
- y < rep (0,n)
- y = 0 0 0 0 0 0 0 0 0 0
R Data Input
Sources (5)
- Text Files (eg. ASCII, XML, webscraping)
- Statistical Packages (eg. SPSS, SAS, Stata)
- Keyboard
- Database Management Systems (eg. MySql, Oracle, Access)
- Other (eg. Excel, NetCFD, HDF5)
Import / Export
Flat Files
Import
- AHW < read.csv(“AHW_1.csv”, header=TRUE)
- weatherdata <-read.table (file=”C:/work/DM1/weather.csv”, header=TRUE, sep=”,”)
Export
write.table(z,”D t RDataFiles Output z.txt”)
Import / Expoort
Databases
Import
connection < dbConnect (driver, user, password, host, dbname
AHW < dbSendQuery (connection, “SELECT * FROM AHW”)
Export
connnection <- dbConnect (driver, user, password, host,dbname
dbWriteTable (connnection , “AHW”, AHW)
Import / Export
R objects
- Import: > load(‘AHW.Rdata’)
- Export: > save(AHW, file= “New_AHW.Rdata”)
Import
Web
connection <- url (‘http://pace.sdsc.edu/sites/bootcamp/images/AHW_1.csv’)
AHW <- read.csv(connection, header=TRUE)
How to enter data in R
5
-
Sequential Data: assignment operator and vector definition (x = 1:5)
2.** Non-sequential Data**: concatenation operator - List Objects
- Read a CSV
- Structure: provides info about data frame
ls()
displays list objects
eg. x = 5, y = 3
ls() = “x” “y”
Read data from a spreadsheet
process
- convert spreadsheet to .csv file
- variable -< read.csv(“Path”)
- need forward slash or 2 back slashes in path
- example variable name: sn.csv
str(csv_variable)
- ## provides details of Data frame from csv file
Data input
keyboard
example
mydata <- data.frame (age=numeric(0), gender=character(0),
weight=numeric(0))
mydata <- edit( mydata)
Data Types
- Vector (1 dimensional)
- Matrix (2 dimensional)
- Array (3 dimensional)
- Data Frame
- Column can be different modes - List
- Vectors, matrix, arrays, data frames, lists
Data Frame
- More general than a matrix
- Different columns can contain different modes of data
- concatenate values for individual columns
variable <- data.frame(column1, column2, column3, etc)
Specifying Data Frame Elements
- patientdata [1:2] = all rows of 1st 2 data columns
- patientdata [ diabetes”,”status”]) = all rows of specified columns
- patientdata$age = all values in age column (without header)
