Histogram of CuDF with groupby fails

ALL software version info

(this library, plus any other relevant software, e.g. bokeh, python, notebook, OS, browser, etc)

hvplot 0.6 bokeh 2.2 cudf 0.15.0a+4572.gafb3928f6 (should be equiv with 0.15 or 0.16)

Description of expected behavior and the observed behavior

hvplot.hist on a CuDF Datframe fails if a by argument is supplied (works without a by argument)

Complete, minimal, self-contained example code that reproduces the issue

import cudf
import hvplot.cudf

df = cudf.DataFrame({"x": [1,2,1,3,4,5], "v": [0,0,0, 1,1,1]})
df.hvplot.hist(y="x", by="v")

Edit: updated “v” column to not be string since CuDF does not support string arrays yet

Stack traceback and/or browser JavaScript console output

TypeError: Series object is not iterable. Consider using `.to_arrow()`, `.to_pandas()` or `.values_host` if you wish to iterate over the values.

``` --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-187-76dbabf783f0> in <module> 1 df = cudf.DataFrame({"x": [1,2,1,3,4,5], "v": list("abaabb")}) ----> 2 df.hvplot.hist(y="x", by="v")

~/anaconda/envs/cuxfdev/lib/python3.7/site-packages/hvplot/plotting/core.py in hist(self, y, by, **kwds) 399 The HoloViews representation of the plot. 400 “”" –> 401 return self(kind=‘hist’, x=None, y=y, by=by, **kwds) 402 403 def kde(self, y=None, by=None, **kwds):

~/anaconda/envs/cuxfdev/lib/python3.7/site-packages/hvplot/plotting/core.py in call(self, x, y, kind, **kwds) 70 return pn.panel(plot, **panel_dict) 71 —> 72 return self._get_converter(x, y, kind, **kwds)(kind, x, y) 73 74 def _get_converter(self, x=None, y=None, kind=None, **kwds):

~/anaconda/envs/cuxfdev/lib/python3.7/site-packages/hvplot/converter.py in call(self, kind, x, y) 1022 dataset = Dataset(data) 1023 dataset = dataset.redim(**self._redim) -> 1024 obj = method(x, y) 1025 obj._dataset = dataset 1026

~/anaconda/envs/cuxfdev/lib/python3.7/site-packages/hvplot/converter.py in hist(self, x, y, data) 1472 if self.by: 1473 hist = hists = histogram( -> 1474 ds.groupby(self.by), dimension=y, **hist_opts 1475 ) 1476 hist = hists.last

~/anaconda/envs/cuxfdev/lib/python3.7/site-packages/holoviews/core/data/init.py in pipelined_fn(*args, **kwargs) 214 215 try: –> 216 result = method_fn(*args, **kwargs) 217 218 op = method_op.instance(

~/anaconda/envs/cuxfdev/lib/python3.7/site-packages/holoviews/core/data/init.py in groupby(self, dimensions, container_type, group_type, dynamic, **kwargs) 969 970 return self.interface.groupby(self, dim_names, container_type, –> 971 group_type, **kwargs) 972 973 def transform(self, *args, **kwargs):

~/anaconda/envs/cuxfdev/lib/python3.7/site-packages/holoviews/core/data/cudf.py in groupby(cls, dataset, dimensions, container_type, group_type, **kwargs) 164 165 # Find all the keys along supplied dimensions –> 166 keys = product(*(dataset.data[dimensions[0]].unique() for d in dimensions)) 167 168 # Iterate over the unique entries applying selection masks

~/anaconda/envs/cuxfdev/lib/python3.7/site-packages/cudf/core/series.py in iter(self) 801 802 def iter(self): –> 803 cudf.utils.utils.raise_iteration_error(obj=self) 804 805 iteritems = iter

~/anaconda/envs/cuxfdev/lib/python3.7/site-packages/cudf/utils/utils.py in raise_iteration_error(obj) 435 def raise_iteration_error(obj): 436 raise TypeError( –> 437 f"{obj.class.name} object is not iterable. " 438 f"Consider using .to_arrow(), .to_pandas() or .values_host " 439 f"if you wish to iterate over the values."

TypeError: Series object is not iterable. Consider using .to_arrow(), .to_pandas() or .values_host if you wish to iterate over the values.

</details>

#### Screenshots or screencasts of the bug in action

[bryevdv]

@philippjfr can you move this to holoviews?

[maximlt]

It seems like this was fixed but never closed 🙃