write tree rules as SQL case when statements

[carlyw]

asSQL prints the decision tree rules in the format of SQL case when statements. Modified labels.rpart and path.rpart to accomodate asSQL needs

[carlyw]

devtools::load_all(".")

(form <- as.formula(paste("Price ~", 
                    paste(setdiff(colnames(car90), "Price"), collapse = "+"))))

(dtree <- rpart(formula = form, data = car90))

asSQL(dtree)

devtools::load_all(".")
## Loading rpart
(form <- as.formula(paste("Price ~",
                         paste(setdiff(colnames(car90), "Price"),
                               collapse = "+"))))
## Price ~ Country + Disp + Disp2 + Eng.Rev + Front.Hd + Frt.Leg.Room + 
##     Frt.Shld + Gear.Ratio + Gear2 + HP + HP.revs + Height + Length + 
##     Luggage + Mileage + Model2 + Rear.Hd + Rear.Seating + RearShld + 
##     Reliability + Rim + Sratio.m + Sratio.p + Steering + Tank + 
##     Tires + Trans1 + Trans2 + Turning + Type + Weight + Wheel.base + 
##     Width
(dtree <- rpart(formula = form, data = car90))
## n=105 (6 observations deleted due to missingness)
## 
## node), split, n, deviance, yval
##       * denotes terminal node
## 
##  1) root 105 7118267000 15805.220  
##    2) Rim=R12,R13,R14 68 1101501000 11487.500  
##      4) Tank< 15.65 36  189145300  8988.278  
##        8) Tires=145,145/80,155,155/65,155/80,165/65,165/80,175/70,185/80 20   31853590  7419.050 *
##        9) Tires=185/60,185/70,195/60,195/70,195/75,205/75 16   46480320 10949.810 *
##      5) Tank>=15.65 32  434528300 14299.120  
##       10) HP< 147.5 25  119553300 13014.720 *
##       11) HP>=147.5 7  126438300 18886.290 *
##    3) Rim=R15,R16,R17 37 2419229000 23740.490  
##      6) HP< 162.5 23  863713000 20147.610  
##       12) Height< 49.75 9   87042290 14755.000 *
##       13) Height>=49.75 14  346698700 23614.290 *
##      7) HP>=162.5 14  770847400 29643.070 *
asSQL(dtree)
## CASE WHEN 
##    Rim in ('R12', 'R13', 'R14')
##     Tank>=15.65
##     HP< 147.5
##    THEN 13014.72
## WHEN 
##    Rim in ('R12', 'R13', 'R14')
##     Tank< 15.65
##     Tires in ('145', '145/80', '155', '155/65', '155/80', '165/65', '165/80', '175/70', '185/80')
##    THEN 7419.05
## WHEN 
##    Rim in ('R12', 'R13', 'R14')
##     Tank< 15.65
##     Tires in ('185/60', '185/70', '195/60', '195/70', '195/75', '205/75')
##    THEN 10949.8125
## WHEN 
##    Rim in ('R15', 'R16', 'R17')
##     HP< 162.5
##     Height>=49.75
##    THEN 23614.2857142857
## WHEN 
##    Rim in ('R15', 'R16', 'R17')
##     HP>=162.5
##    THEN 29643.0714285714
## WHEN 
##    Rim in ('R15', 'R16', 'R17')
##     HP< 162.5
##     Height< 49.75
##    THEN 14755
## WHEN 
##    Rim in ('R12', 'R13', 'R14')
##     Tank>=15.65
##     HP>=147.5
##    THEN 18886.2857142857

^{Created on 2019-04-23 by the reprex package (v0.2.1)}