[SPARKR][EXAMPLES] update examples to stop spark session

## What changes were proposed in this pull request?

stop session at end of example

## How was this patch tested?

manual

Author: Felix Cheung <felixcheung_m@hotmail.com>

Closes #16973 from felixcheung/rexamples.

examples/src/main/r/ml/als.R

@@ -41,5 +41,7 @@ summary(model)
 
 # Prediction
 predictions <- predict(model, test)
-showDF(predictions)
+head(predictions)
 # $example off$
+
+sparkR.session.stop()

examples/src/main/r/ml/bisectingKmeans.R

@@ -40,3 +40,5 @@ summary(fitted.model)
 fitted <- predict(model, df)
 head(select(fitted, "Sepal_Length", "prediction"))
 # $example off$
+
+sparkR.session.stop()

examples/src/main/r/ml/gaussianMixture.R

@@ -38,5 +38,7 @@ summary(model)
 
 # Prediction
 predictions <- predict(model, test)
-showDF(predictions)
+head(predictions)
 # $example off$
+
+sparkR.session.stop()

examples/src/main/r/ml/gbt.R

@@ -40,7 +40,7 @@ summary(model)
 
 # Prediction
 predictions <- predict(model, test)
-showDF(predictions)
+head(predictions)
 # $example off:classification$
 
 # GBT regression model
@@ -59,5 +59,7 @@ summary(model)
 
 # Prediction
 predictions <- predict(model, test)
-showDF(predictions)
+head(predictions)
 # $example off:regression$
+
+sparkR.session.stop()

examples/src/main/r/ml/glm.R

@@ -36,7 +36,7 @@ summary(gaussianGLM)
 
 # Prediction
 gaussianPredictions <- predict(gaussianGLM, gaussianTestDF)
-showDF(gaussianPredictions)
+head(gaussianPredictions)
 
 # Fit a generalized linear model with glm (R-compliant)
 gaussianGLM2 <- glm(Sepal_Length ~ Sepal_Width + Species, gaussianDF, family = "gaussian")
@@ -53,5 +53,7 @@ summary(binomialGLM)
 
 # Prediction
 binomialPredictions <- predict(binomialGLM, binomialTestDF)
-showDF(binomialPredictions)
+head(binomialPredictions)
 # $example off$
+
+sparkR.session.stop()

examples/src/main/r/ml/isoreg.R

@@ -38,5 +38,7 @@ summary(model)
 
 # Prediction
 predictions <- predict(model, test)
-showDF(predictions)
+head(predictions)
 # $example off$
+
+sparkR.session.stop()

examples/src/main/r/ml/kmeans.R

@@ -36,9 +36,11 @@ kmeansModel <- spark.kmeans(kmeansDF, ~ Sepal_Length + Sepal_Width + Petal_Lengt
 summary(kmeansModel)
 
 # Get fitted result from the k-means model
-showDF(fitted(kmeansModel))
+head(fitted(kmeansModel))
 
 # Prediction
 kmeansPredictions <- predict(kmeansModel, kmeansTestDF)
-showDF(kmeansPredictions)
+head(kmeansPredictions)
 # $example off$
+
+sparkR.session.stop()

examples/src/main/r/ml/kstest.R

@@ -37,3 +37,5 @@ model <- spark.kstest(df, "test", "norm")
 # Model summary
 summary(model)
 # $example off$
+
+sparkR.session.stop()

examples/src/main/r/ml/lda.R

@@ -38,9 +38,11 @@ summary(model)
 
 # Posterior probabilities
 posterior <- spark.posterior(model, test)
-showDF(posterior)
+head(posterior)
 
 # The log perplexity of the LDA model
 logPerplexity <- spark.perplexity(model, test)
 print(paste0("The upper bound bound on perplexity: ", logPerplexity))
 # $example off$
+
+sparkR.session.stop()

examples/src/main/r/ml/logit.R

@@ -40,7 +40,7 @@ summary(model)
 
 # Prediction
 predictions <- predict(model, test)
-showDF(predictions)
+head(predictions)
 # $example off:binomial$
 
 # Multinomial logistic regression
@@ -59,5 +59,7 @@ summary(model)
 
 # Prediction
 predictions <- predict(model, test)
-showDF(predictions)
+head(predictions)
 # $example off:multinomial$
+
+sparkR.session.stop()

examples/src/main/r/ml/ml.R

@@ -42,7 +42,7 @@ summary(gaussianGLM2)
 
 # Check model prediction
 gaussianPredictions <- predict(gaussianGLM2, gaussianTestDF)
-showDF(gaussianPredictions)
+head(gaussianPredictions)
 
 unlink(modelPath)
 # $example off:read_write$

examples/src/main/r/ml/mlp.R

@@ -44,5 +44,7 @@ summary(model)
 
 # Prediction
 predictions <- predict(model, test)
-showDF(predictions)
+head(predictions)
 # $example off$
+
+sparkR.session.stop()

examples/src/main/r/ml/naiveBayes.R

@@ -37,5 +37,7 @@ summary(nbModel)
 
 # Prediction
 nbPredictions <- predict(nbModel, nbTestDF)
-showDF(nbPredictions)
+head(nbPredictions)
 # $example off$
+
+sparkR.session.stop()

examples/src/main/r/ml/randomForest.R

@@ -40,7 +40,7 @@ summary(model)
 
 # Prediction
 predictions <- predict(model, test)
-showDF(predictions)
+head(predictions)
 # $example off:classification$
 
 # Random forest regression model
@@ -59,5 +59,7 @@ summary(model)
 
 # Prediction
 predictions <- predict(model, test)
-showDF(predictions)
+head(predictions)
 # $example off:regression$
+
+sparkR.session.stop()

examples/src/main/r/ml/survreg.R

@@ -39,5 +39,7 @@ summary(aftModel)
 
 # Prediction
 aftPredictions <- predict(aftModel, aftTestDF)
-showDF(aftPredictions)
+head(aftPredictions)
 # $example off$
+
+sparkR.session.stop()