How do you interpret this code:
"Training confusion matrix"
predicted <- predict(tree, type = "prob")[,1]
predicted.final <- as.factor(ifelse(predicted > 0.5, "Fail", "Pass"))
confusionMatrix(predicted.final, factor(dataset$Pass.Flag))
what does the [,1] mean in the first row?
The predict function is returning an object predicted with a lot of information packed into it, which you can see with your code with str (predicted) Since I don't know what object tree is, I can't give you the specifics (see FAQ: What's a reproducible example (`reprex`) and how do I do one?), but there are whole lot of possible components. Run (from 'help(predict)`
for(fn in methods("predict"))
try({
f <- eval(substitute(getAnywhere(fn)$objs[[1]], list(fn = fn)))
cat(fn, ":\n\t", deparse(args(f)), "\n")
}, silent = TRUE)
In any even [,1] is a "slice" of the second column of the data packed into a list-like object of the result of running the function predict.
thank you, i've tried the str(predicted), but not sure what this means:
Named num [1:140] 0.6974 0.0992 0.6974 0.6974 0.2473 ...
the first row looks like the probability for each observation.
what does attr(*, "names") mean?
It means that the first component of prediction is a list of 140 numbers and their corresponding labels, generically an attr. If you run
predicted <- predict(tree, type = "prob")
without the trailing slice, you can see the structure of the entire object.
ah, got it. Thank you!
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