# Generate and Retrieve Many Objects with Sequential Names

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While coding ensemble methods in data mining with R, e.g. bagging, we often need to generate many data and models objects with sequential names. Below is a quick example how to use **assign()** function to generate many prediction objects on the fly and then retrieve these predictions with **mget()** to do the model averaging.

data(Boston, package = "MASS") for (i in 1:10) { set.seed(i) smp <- Boston[sample(1:nrow(Boston), nrow(Boston), replace = TRUE), ] glm <- glm(medv ~ ., data = smp) prd <- predict(glm, Boston) ### ASSIGN A LIST OF SEQUENTIAL NAMES TO PREDICTIONS ### assign(paste("p", i, sep = ""), prd) } ### RETURN NAMED OBJECTS TO A LIST ### plist <- mget(paste('p', 1:i, sep = '')) ### AGGREGATE ALL PREDICTIONS ### pcols <- do.call('cbind', plist) pred_medv <- rowSums(pcols) / i ### A SIMPLE FUNCTION CALCULATION R-SQUARE ### r2 <- function(y, yhat) { ybar <- mean(y) r2 <- sum((yhat - ybar) ^ 2) / sum((y - ybar) ^ 2) return(r2) } print(r2(Boston$medv, pred_medv)) # OUTPUT: # [1] 0.7454225

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