Thanks a lot Matthias. Following up with your suggestions, I tried option 2:
# option 2: via removeEmpty
Ind = (X[,1]>10);
Y = removeEmpty(target=X, select=Ind);
SystemML throws a complaint (maybe I'm not using the correct version?):
Named parameter 'margin' missing. Please specify 'rows' or 'cols'.
It works correctly after adding the 'margin' argument:
# option 2: via removeEmpty
Ind = (X[,1]>10);
Y = removeEmpty(target=X, margin = "rows", select=Ind);
I know the document is being updated continuously, just want to point out
the help file for 'removeEmpty()' (link below) does not contain an
explanation of the 'select' argument yet:)
http://apache.github.io/incubatorsystemml/dmllanguagereference.html#matrixconstructionmanipulationandaggregationbuiltinfunctions
Thanks again for your help
Best,
Ethan
On Sun, Apr 3, 2016 at 12:45 AM, Matthias Boehm <mboehm@us.ibm.com> wrote:
> absolutely, if your want to count or aggregate values of the two groups,
> you should definitely go with the aggregate() call instead. The snippets I
> provided are just for the case where you want to run some other analysis
> over the subsets (e.g., running an algorithm over a sample or fold).
>
> Regards,
> Matthias
>
>
> [image: Inactive hide details for Ethan Xu 03/31/2016 11:31:32 AMAh
> I missed the 'removeEmpty()' function. That's a smart ways to]Ethan Xu
> 03/31/2016 11:31:32 AMAh I missed the 'removeEmpty()' function.
> That's a smart ways to trim matrix. Thanks Matthias!
>
> From: Ethan Xu <ethan.yifanxu@gmail.com>
> To: dev@systemml.incubator.apache.org
> Date: 03/31/2016 11:31 AM
> Subject: Re: Logical indexing?
> 
>
>
>
> Ah I missed the 'removeEmpty()' function. That's a smart ways to trim
> matrix. Thanks Matthias!
>
> Also from your answer I realized 'ind = (X[,1] > 10);' is acceptable, so
> aggregation would work with
>
> ind = (X[,1] > 10) + 1;
> F = aggregate(target = X[,2], groups = ind, fn = "sum");
>
> Ethan
>
>
> On Thu, Mar 31, 2016 at 1:22 PM, Matthias Boehm <mboehm@us.ibm.com> wrote:
>
> > just a quick correction of option 2:
> >
> > Ind = (X[,1]>10);
> > Y = removeEmpty(target=X, select=Ind);
> >
> > Regards,
> > Matthias
> >
> > [image: Inactive hide details for Matthias Boehm03/31/2016 10:14:50
> > AMthat's a good question  no SystemML does not support set i]Matthias
> > Boehm03/31/2016 10:14:50 AMthat's a good question  no SystemML
> does
> > not support set indexing yet but you can emulate it via pe
> >
> > From: Matthias Boehm/Almaden/IBM@IBMUS
> > To: dev@systemml.incubator.apache.org
> > Date: 03/31/2016 10:14 AM
> > Subject: Re: Logical indexing?
> > 
> >
> >
> >
> > that's a good question  no SystemML does not support set indexing yet
> but
> > you can emulate it via permutation matrices or similar transformations.
> > Here are some examples:
> >
> > # option 1: via permutation (aka selection) matrices
> > P = removeEmpty(target=diag(X[,1]>10), margin="rows");
> > Y = P %*% X;
> >
> > # option 2: via removeEmpty
> > Ind = diag(X[,1]>10);
> > Y = removeEmpty(target=X, select=Ind);
> >
> >
> > Regards,
> > Matthias
> >
> > Ethan Xu 03/31/2016 08:47:43 AMDoes SystemML support logical
> > indexing? For example if X is a numerical matrix with 2 columns and n
> >
> > From: Ethan Xu <ethan.yifanxu@gmail.com>
> > To: dev@systemml.incubator.apache.org
> > Date: 03/31/2016 08:47 AM
> > Subject: Logical indexing?
> > 
> >
> >
> >
> > Does SystemML support logical indexing?
> >
> > For example if X is a numerical matrix with 2 columns and n rows (in my
> > case n ~ 35 million). I'd like to split the matrix rowwise according to
> > values of the first column. This is useful when I need to find
> > distributions of subgroups of population. In R I can do
> >
> > Y = X[ X[ ,1] > 10, ]
> >
> > OR
> >
> > ind = which(X[ ,1] > 10)
> > Y = X[ind, ]
> >
> > It seems neither syntex works in SystemML.
> >
> > I noticed there's an aggregate() function for SystemML, but it supports
> > coded categorical variable.
> >
> > Perhaps one way to do that is creating an indicator n by 1 matrix Z that
> > takes values 1 and 2 where 1 corresponds to X[, 1] <= 10 and 2
> corresponds
> > to X[,1] > 10. Then aggregate() X[,2] with respect to Z.
> >
> > It seems transform() with 'bin' option is one obvious way to create such
> a
> > Z, however the 'bin' method only supports 'equiwidth' currently.
> >
> > Is looping through X[,1] the best option? Maybe I missed some other
> > convenient functions.
> >
> > Any suggestions are greatly appreciated!
> >
> > Best,
> >
> > Ethan
> >
> >
> >
> >
>
>
>
