ISLR Lab 4.6
David Veitch
18/10/2019
library(ISLR)
# setwd('C:/Users/davev/Google Drive/Documents/UofT/TA/2019 314/Tutorial 6')
# write.csv(Smarket,file='Smarket.csv',row.names=FALSE)
Smarket = read.csv(file='Smarket.csv')Look at data
names(Smarket)## [1] "Year" "Lag1" "Lag2" "Lag3" "Lag4" "Lag5"
## [7] "Volume" "Today" "Direction"dim(Smarket)## [1] 1250 9summary(Smarket)## Year Lag1 Lag2
## Min. :2001 Min. :-4.922000 Min. :-4.922000
## 1st Qu.:2002 1st Qu.:-0.639500 1st Qu.:-0.639500
## Median :2003 Median : 0.039000 Median : 0.039000
## Mean :2003 Mean : 0.003834 Mean : 0.003919
## 3rd Qu.:2004 3rd Qu.: 0.596750 3rd Qu.: 0.596750
## Max. :2005 Max. : 5.733000 Max. : 5.733000
## Lag3 Lag4 Lag5
## Min. :-4.922000 Min. :-4.922000 Min. :-4.92200
## 1st Qu.:-0.640000 1st Qu.:-0.640000 1st Qu.:-0.64000
## Median : 0.038500 Median : 0.038500 Median : 0.03850
## Mean : 0.001716 Mean : 0.001636 Mean : 0.00561
## 3rd Qu.: 0.596750 3rd Qu.: 0.596750 3rd Qu.: 0.59700
## Max. : 5.733000 Max. : 5.733000 Max. : 5.73300
## Volume Today Direction
## Min. :0.3561 Min. :-4.922000 Down:602
## 1st Qu.:1.2574 1st Qu.:-0.639500 Up :648
## Median :1.4229 Median : 0.038500
## Mean :1.4783 Mean : 0.003138
## 3rd Qu.:1.6417 3rd Qu.: 0.596750
## Max. :3.1525 Max. : 5.733000Look at pairwise correlations
cor(Smarket)## Error in cor(Smarket): 'x' must be numericcor(Smarket[,-9])## Year Lag1 Lag2 Lag3 Lag4
## Year 1.00000000 0.029699649 0.030596422 0.033194581 0.035688718
## Lag1 0.02969965 1.000000000 -0.026294328 -0.010803402 -0.002985911
## Lag2 0.03059642 -0.026294328 1.000000000 -0.025896670 -0.010853533
## Lag3 0.03319458 -0.010803402 -0.025896670 1.000000000 -0.024051036
## Lag4 0.03568872 -0.002985911 -0.010853533 -0.024051036 1.000000000
## Lag5 0.02978799 -0.005674606 -0.003557949 -0.018808338 -0.027083641
## Volume 0.53900647 0.040909908 -0.043383215 -0.041823686 -0.048414246
## Today 0.03009523 -0.026155045 -0.010250033 -0.002447647 -0.006899527
## Lag5 Volume Today
## Year 0.029787995 0.53900647 0.030095229
## Lag1 -0.005674606 0.04090991 -0.026155045
## Lag2 -0.003557949 -0.04338321 -0.010250033
## Lag3 -0.018808338 -0.04182369 -0.002447647
## Lag4 -0.027083641 -0.04841425 -0.006899527
## Lag5 1.000000000 -0.02200231 -0.034860083
## Volume -0.022002315 1.00000000 0.014591823
## Today -0.034860083 0.01459182 1.000000000attach(Smarket)
plot(Volume)
Fit a GLM
glm.fits = glm(Direction~Lag1+Lag2+Lag3+Lag4+Lag5+Volume,
data=Smarket,
family=binomial)
summary(glm.fits)##
## Call:
## glm(formula = Direction ~ Lag1 + Lag2 + Lag3 + Lag4 + Lag5 +
## Volume, family = binomial, data = Smarket)
##
## Deviance Residuals:
## Min 1Q Median 3Q Max
## -1.446 -1.203 1.065 1.145 1.326
##
## Coefficients:
## Estimate Std. Error z value Pr(>|z|)
## (Intercept) -0.126000 0.240736 -0.523 0.601
## Lag1 -0.073074 0.050167 -1.457 0.145
## Lag2 -0.042301 0.050086 -0.845 0.398
## Lag3 0.011085 0.049939 0.222 0.824
## Lag4 0.009359 0.049974 0.187 0.851
## Lag5 0.010313 0.049511 0.208 0.835
## Volume 0.135441 0.158360 0.855 0.392
##
## (Dispersion parameter for binomial family taken to be 1)
##
## Null deviance: 1731.2 on 1249 degrees of freedom
## Residual deviance: 1727.6 on 1243 degrees of freedom
## AIC: 1741.6
##
## Number of Fisher Scoring iterations: 3Access coefficients
coef(glm.fits)## (Intercept) Lag1 Lag2 Lag3 Lag4
## -0.126000257 -0.073073746 -0.042301344 0.011085108 0.009358938
## Lag5 Volume
## 0.010313068 0.135440659summary(glm.fits)$coef## Estimate Std. Error z value Pr(>|z|)
## (Intercept) -0.126000257 0.24073574 -0.5233966 0.6006983
## Lag1 -0.073073746 0.05016739 -1.4565986 0.1452272
## Lag2 -0.042301344 0.05008605 -0.8445733 0.3983491
## Lag3 0.011085108 0.04993854 0.2219750 0.8243333
## Lag4 0.009358938 0.04997413 0.1872757 0.8514445
## Lag5 0.010313068 0.04951146 0.2082966 0.8349974
## Volume 0.135440659 0.15835970 0.8552723 0.3924004Use predict function to access predicted probabilities and print some sample probabilities
glm.probs=predict(glm.fits,type='response')
glm.probs[1:10]## 1 2 3 4 5 6 7
## 0.5070841 0.4814679 0.4811388 0.5152224 0.5107812 0.5069565 0.4926509
## 8 9 10
## 0.5092292 0.5176135 0.4888378Logistic regression predicting direction, but direction a categorical variable! Use contrasts to check which category corresponds to 1 and 0.
contrasts(Smarket$Direction)## Up
## Down 0
## Up 1Translate predictions back into Up/Down
glm.pred=rep("Down",1250)
glm.pred[glm.probs>.5]="Up"Compare predictions to reality
table(glm.pred,Direction)## Direction
## glm.pred Down Up
## Down 145 141
## Up 457 507mean(glm.pred==Direction)## [1] 0.5216Lets try to split this up into training and testing data to better see how accuracy is.
train=(Year<2005)
Smarket.2005 = Smarket[!train,]
Direction.2005 = Direction[!train]
dim(Smarket.2005)## [1] 252 9Fit a model to just training data using subset command
glm.fits = glm(Direction~Lag1+Lag2+Lag3+Lag4+Lag5+Volume,
data=Smarket,
family=binomial,
subset = train)
glm.probs = predict(glm.fits,Smarket.2005,type="response")
glm.pred=rep("Down",252)
glm.pred[glm.probs>.5]="Up"
table(glm.pred,Direction.2005)## Direction.2005
## glm.pred Down Up
## Down 77 97
## Up 34 44Performance not so good, check the average accuracy
mean(glm.pred==Direction.2005)## [1] 0.4801587Maybe we can mprove our model by only including Lag1 and Lag2 which were the most statistically significant
glm.fits = glm(Direction~Lag1+Lag2,
data=Smarket,
family=binomial,
subset = train)
glm.probs = predict(glm.fits,Smarket.2005,type="response")
glm.pred=rep("Down",252)
glm.pred[glm.probs>.5]="Up"
table(glm.pred,Direction.2005)## Direction.2005
## glm.pred Down Up
## Down 35 35
## Up 76 106mean(glm.pred==Direction.2005)## [1] 0.5595238A much better performance. Perhaps the more complex model was overfitting!