Access to axis label's values conditionaly filtered on data values

[tim-evain]

Hi,

I'm trying to retrieve axis label values of data that fit a certain condition. With xarray (python) I would go with something like:

import numpy as np
import xarray as xr

data = xr.DataArray(np.random.random([5,2,2]),dims=('time','slice','biomarker'),coords={'time':[0,5,10,15,20],'slice':['-0.15','0.15'],'biomarker':['A','B']})
filt_data = data.where(data>0.5,drop=True)
retrieved_labels = []
for time_i in filt_data.time:
    for slice_i in filt_data.slice:
        for bio_i in filt_data.biomarker:
            if not filt_data.sel(time=time_i,slice=slice_i,biomarker=bio_i).isnull():
                retrieved_labels.append((time_i.values[()],slice_i.values[()],bio_i.values[()]))

but I'm failing to replicate that through xframe on multiple aspects:

xf::xaxis<int>
     time_axis = xf::axis({ 0,5,10,15,20 });
xf::xaxis<xf::fstring>
     slice_axis = xf::axis({ "-0.15", "0.15" }),
     biomarker_axis = xf::axis({ "A", "B" });
xf::xcoordinate<xf::fstring> coord_descriptor({ {"Time", time_axis}, {"Location", slice_axis},  {"Biomarker", biomarker_axis } });
xf::xdimension<xf::fstring> dim_organizer({ "Time", "SliceLocation", "Biomarker" }); 
xf::xvariable<double, xf::xcoordinate<xf::fstring>>::data_type data = xt::eval(xt::random::rand({ 5, 2, 2 }, 0., 1.));
xf::xvariable<double, xf::xcoordinate<xf::fstring>> data_array(data,coord_descriptor, dim_organizer);

//Axis values can later be fetched through:
auto t_axis = data_array.coordinates()["Time"];
std::vector<xf::fstring> all_labels = xf::get_labels<xf::fstring>(t_axis);
// or
xf::fstring label_X = xtl::xget<xf::fstring>(t_axis.label(X));

My bet was to go with masking with something like xf::where(data_array, data_array > 0.5), but that's not working since xf::where seems a filter on label and not data.

What would be the best way to achieve that?

Also, when looking for comparison operator, I wasn't able to find xf::greater and like functions in the code (from the "From xarray to xframe" documentation). I guess they are still under development?