…istently print the metrics on driver's stdout
### What changes were proposed in this pull request?
Call collect on RDD before calling foreach so that it sends the result to the driver node and print it on this node's stdout.
### Why are the changes needed?
Some RDDs in this example (e.g., precision, recall) call println without calling collect.
If the job is under local mode, it sends the data to the driver node and prints the metrics on the driver's stdout.
However if the job is under cluster mode, the job prints the metrics on the executor's stdout.
It seems inconsistent compared to the other metrics nothing to do with RDD (e.g., auPRC, auROC) since these metrics always output the result on the driver's stdout.
All of the metrics should output its result on the driver's stdout.
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
This is example code. It doesn't have any tests.
Closes#29222 from titsuki/SPARK-32428.
Authored-by: Itsuki Toyota <titsuki@cpan.org>
Signed-off-by: Sean Owen <srowen@gmail.com>
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