library(MASS)
data(petrol)
data(Cars93)
head(petrol)

Rename

names(petrol) <- c("ID", "SpecGrav", "VaporPressure", "VolCrude", "VolGas", "PercCrude" )
head(petrol)

Order()

The order() gives a vector of numbers relating to a row

order(petrol$VaporPressure)
##  [1] 30 31 32 25 26 27 21 22 23 24 28 29  5  6  7 15 16 17 18 19 20  8  9
## [24] 10 11 12 13 14  1  2  3  4

Use in subsetting to rearrange a data frame from lowest to highest

petrol[order(petrol$VaporPressure),]

Decreasing order

petrol[order(petrol$VaporPressure,decreasing=TRUE),]

Order by multiple variables – first by vapor pressure then volatility of gas

petrol[order(petrol$VaporPressure, petrol$VolGas, decreasing = T),]

Create a new dataset ordered by

newpetrol <- petrol[order(petrol$PercCrude, decreasing = T),]
newpetrol

Reorder columns (ex. alphabetical order)

newpetrol <- newpetrol[,order(names(petrol))] 
newpetrol

Which()

Cars93[, c("Model", "Type", "Price")]

A logical function that returns matching values that makes the statement True

Cars93[,which(colnames(Cars93)=="Model")]
##  [1] Integra        Legend         90             100           
##  [5] 535i           Century        LeSabre        Roadmaster    
##  [9] Riviera        DeVille        Seville        Cavalier      
## [13] Corsica        Camaro         Lumina         Lumina_APV    
## [17] Astro          Caprice        Corvette       Concorde      
## [21] LeBaron        Imperial       Colt           Shadow        
## [25] Spirit         Caravan        Dynasty        Stealth       
## [29] Summit         Vision         Festiva        Escort        
## [33] Tempo          Mustang        Probe          Aerostar      
## [37] Taurus         Crown_Victoria Metro          Storm         
## [41] Prelude        Civic          Accord         Excel         
## [45] Elantra        Scoupe         Sonata         Q45           
## [49] ES300          SC300          Continental    Town_Car      
## [53] 323            Protege        626            MPV           
## [57] RX-7           190E           300E           Capri         
## [61] Cougar         Mirage         Diamante       Sentra        
## [65] Altima         Quest          Maxima         Achieva       
## [69] Cutlass_Ciera  Silhouette     Eighty-Eight   Laser         
## [73] LeMans         Sunbird        Firebird       Grand_Prix    
## [77] Bonneville     900            SL             Justy         
## [81] Loyale         Legacy         Swift          Tercel        
## [85] Celica         Camry          Previa         Fox           
## [89] Eurovan        Passat         Corrado        240           
## [93] 850           
## 93 Levels: 100 190E 240 300E 323 535i 626 850 90 900 Accord ... Vision

Subset by rows and columns simultaneously

Cars93[which(Cars93$Cylinders==8), c("Model", "Price")]

Get the mean price of 8 cylinder cars

mean(Cars93[which(Cars93$Cylinders==8), "Price"])
## [1] 33.78571

Create new data

Forddata <- Cars93[-which(Cars93$Manufacturer=="Ford"), c("Model", "Price", "MPG.city", "Cylinders")]
Forddata

Exclude data

Forddata[-which(Forddata$Cylinders == 6),]