@shrit noticed that the mlpack_knn binding would produce strange output when loading data:

$ ./bin/mlpack_knn -r ~/datasets/corel.csv -q ~/datasets/corel.csv -k 3 -v
[INFO ] Using reference data from Loading '/home/ryan/datasets/corel.csv' as CSV data.  Size is 32 x 37749.
[INFO ] '/home/ryan/datasets/corel.csv' (37749x32 matrix).
[INFO ] Building reference tree...
[INFO ] Tree built.
[INFO ] Using query data from Loading '/home/ryan/datasets/corel.csv' as CSV data.  Size is 32 x 37749.
[INFO ] '/home/ryan/datasets/corel.csv' (37749x32 matrix).
[INFO ] Searching for 3 neighbors with dual-tree kd-tree search...

You can see from the output that the first message is actually two messages being printed at the same time.

I dug into this and it is a strange artifact of how the command-line bindings work---the problem does not show up for other binding types. The issue is this:

• For command-line bindings, we call data::Load() the first time a parameter is accessed (e.g. params.Get<arma::mat>("matrix") or params.GetPrintable<arma::mat>("matrix")), and that call to data::Load() will produce output.
• But in some bindings, the call to GetPrintable<> is used to print a status message.
• If GetPrintable<> is called on a matrix parameter before the data has been loaded, then the data::Load() message will be printed while that GetPrintable<> call happens... leading to the duplicate message.

So, I found all bindings where this situation happens, and where possible I changed things around so that GetPrintable<> was not the first call that would trigger the load of a matrix. So long as the first call is something like params.Get<arma::mat>("matrix"), then the load happens separately and there is no duplicate output.

After this PR the output of the program command above is:

[INFO ] Loading '/home/ryan/datasets/corel.csv' as CSV data.  Size is 32 x 37749.
[INFO ] Using reference data from '/home/ryan/datasets/corel.csv' (37749x32 matrix).
[INFO ] Building reference tree...
[INFO ] Tree built.
[INFO ] Loading '/home/ryan/datasets/corel.csv' as CSV data.  Size is 32 x 37749.
[INFO ] Using query data from '/home/ryan/datasets/corel.csv' (37749x32 matrix).
[INFO ] Searching for 3 neighbors with dual-tree kd-tree search...

which is what we would hope for.