diff --git a/upsetplot/plotting.py b/upsetplot/plotting.py
index ff693e7..a8b7ba1 100644
--- a/upsetplot/plotting.py
+++ b/upsetplot/plotting.py
@@ -84,11 +84,29 @@ def _aggregate_data(df, subset_size, sum_over):
     return df, aggregated
 
 
+def _check_index(df):
+    # check all indices are boolean
+    if not all(set([True, False]) >= set(level)
+               for level in df.index.levels):
+        raise ValueError('The DataFrame has values in its index that are not '
+                         'boolean')
+    df = df.copy(deep=False)
+    # XXX: this may break if input is not MultiIndex
+    kw = {'levels': [x.astype(bool) for x in df.index.levels],
+          'names': df.index.names,
+          }
+    if hasattr(df.index, 'codes'):
+        # compat for pandas <= 0.20
+        kw['codes'] = df.index.codes
+    else:
+        kw['labels'] = df.index.labels
+    df.index = pd.MultiIndex(**kw)
+    return df
+
+
 def _process_data(df, sort_by, sort_categories_by, subset_size, sum_over):
     df, agg = _aggregate_data(df, subset_size, sum_over)
-
-    # check all indices are boolean
-    assert all(set([True, False]) >= set(level) for level in agg.index.levels)
+    df = _check_index(df)
 
     totals = [agg[agg.index.get_level_values(name).values.astype(bool)].sum()
               for name in agg.index.names]

Allow truthy/falsy index?
I have a pandas dataframe with 1 or 0 as valued for dummied columns. When I try to plot without changing the 1/0 to True/False the figure is missing the dot grid/connections. Is this by design, and is it possible to allow the 1/0?

Below is an example to reproduce. The line with the comment is the one to include/remove to see the difference. Including images of the output for each below as well.

```
import pandas as pd
from matplotlib import pyplot as plt
from upsetplot import plot

df = pd.DataFrame({"unique_id": [1, 2, 3, 4, 5, 6, 7], "a": [1, 1, 1, 0, 1, 0, 0], "b": [1, 0, 0, 0, 1, 0, 0], "c": [1, 0, 1, 0, 1, 0, 0]})
df = df.replace({0: False, 1: True})  # different results with/without this conversion
plot_df = df.fillna(False).groupby(["a", "b", "c"]).count()['unique_id']
plot(plot_df)
pyplot.show()
```

Without the conversion to True/False:
![Screen Shot 2019-08-13 at 6 49 26 PM](https://user-images.githubusercontent.com/19669890/62985126-7a6e4a00-bdfb-11e9-9121-57026e924966.png)

With the conversion to True/False:
![Screen Shot 2019-08-13 at 6 49 38 PM](https://user-images.githubusercontent.com/19669890/62985121-76422c80-bdfb-11e9-90a2-e07c73a4e2f7.png)

diff --git a/upsetplot/tests/test_upsetplot.py b/upsetplot/tests/test_upsetplot.py
index a216e72..66bc50b 100644
--- a/upsetplot/tests/test_upsetplot.py
+++ b/upsetplot/tests/test_upsetplot.py
@@ -439,3 +439,22 @@ def test_add_catplot():
     upset.add_catplot('foobar', value='foo')
     with pytest.raises(AttributeError):
         upset.plot(fig)
+
+
+@pytest.mark.parametrize('x', [
+    generate_counts(),
+])
+def test_index_must_be_bool(x):
+    # Truthy ints are okay
+    x = x.reset_index()
+    x[['cat0', 'cat2', 'cat2']] = x[['cat0', 'cat1', 'cat2']].astype(int)
+    x = x.set_index(['cat0', 'cat1', 'cat2']).iloc[:, 0]
+
+    UpSet(x)
+
+    # other ints are not
+    x = x.reset_index()
+    x[['cat0', 'cat2', 'cat2']] = x[['cat0', 'cat1', 'cat2']] + 1
+    x = x.set_index(['cat0', 'cat1', 'cat2']).iloc[:, 0]
+    with pytest.raises(ValueError, match='not boolean'):
+        UpSet(x)

pip install -e .[dev]
parse_log_pytest
requirements.txt
pytest pytest-cov
apt-get update apt-get install -y gcc
3.6
doc/requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
alabaster==0.7.13
attrs==22.2.0
Babel==2.11.0
certifi==2021.5.30
charset-normalizer==2.0.12
coverage==6.2
cycler==0.11.0
docutils==0.18.1
idna==3.10
imagesize==1.4.1
importlib-metadata==4.8.3
iniconfig==1.1.1
Jinja2==3.0.3
joblib==1.1.1
kiwisolver==1.3.1
MarkupSafe==2.0.1
matplotlib==3.3.4
numpy==1.19.5
numpydoc==1.1.0
packaging==21.3
pandas==1.1.5
Pillow==8.4.0
pluggy==1.0.0
py==1.11.0
Pygments==2.14.0
pyparsing==3.1.4
pytest==7.0.1
pytest-cov==4.0.0
python-dateutil==2.9.0.post0
pytz==2025.2
requests==2.27.1
scikit-learn==0.24.2
scipy==1.5.4
seaborn==0.11.2
six==1.17.0
snowballstemmer==2.2.0
Sphinx==5.3.0
sphinx-gallery==0.10.0
sphinx-issues==3.0.1
sphinxcontrib-applehelp==1.0.2
sphinxcontrib-devhelp==1.0.2
sphinxcontrib-htmlhelp==2.0.0
sphinxcontrib-jsmath==1.0.1
sphinxcontrib-qthelp==1.0.3
sphinxcontrib-serializinghtml==1.1.5
threadpoolctl==3.1.0
tomli==1.2.3
typing_extensions==4.1.1
-e git+https://github.com/jnothman/UpSetPlot.git@ad83089d04cde701b70e5260d18ea619a2c337fb#egg=UpSetPlot
urllib3==1.26.20
zipp==3.6.0

name: UpSetPlot
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - pip=21.2.2=py36h06a4308_0
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - setuptools=58.0.4=py36h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - alabaster==0.7.13
      - attrs==22.2.0
      - babel==2.11.0
      - charset-normalizer==2.0.12
      - coverage==6.2
      - cycler==0.11.0
      - docutils==0.18.1
      - idna==3.10
      - imagesize==1.4.1
      - importlib-metadata==4.8.3
      - iniconfig==1.1.1
      - jinja2==3.0.3
      - joblib==1.1.1
      - kiwisolver==1.3.1
      - markupsafe==2.0.1
      - matplotlib==3.3.4
      - numpy==1.19.5
      - numpydoc==1.1.0
      - packaging==21.3
      - pandas==1.1.5
      - pillow==8.4.0
      - pluggy==1.0.0
      - py==1.11.0
      - pygments==2.14.0
      - pyparsing==3.1.4
      - pytest==7.0.1
      - pytest-cov==4.0.0
      - python-dateutil==2.9.0.post0
      - pytz==2025.2
      - requests==2.27.1
      - scikit-learn==0.24.2
      - scipy==1.5.4
      - seaborn==0.11.2
      - six==1.17.0
      - snowballstemmer==2.2.0
      - sphinx==5.3.0
      - sphinx-gallery==0.10.0
      - sphinx-issues==3.0.1
      - sphinxcontrib-applehelp==1.0.2
      - sphinxcontrib-devhelp==1.0.2
      - sphinxcontrib-htmlhelp==2.0.0
      - sphinxcontrib-jsmath==1.0.1
      - sphinxcontrib-qthelp==1.0.3
      - sphinxcontrib-serializinghtml==1.1.5
      - threadpoolctl==3.1.0
      - tomli==1.2.3
      - typing-extensions==4.1.1
      - urllib3==1.26.20
      - zipp==3.6.0
prefix: /opt/conda/envs/UpSetPlot

upsetplot/tests/test_upsetplot.py::test_index_must_be_bool[x0]
upsetplot/tests/test_upsetplot.py::test_process_data_series[None-cardinality-x0] upsetplot/tests/test_upsetplot.py::test_process_data_series[None-cardinality-x1] upsetplot/tests/test_upsetplot.py::test_process_data_series[None-degree-x0] upsetplot/tests/test_upsetplot.py::test_process_data_series[None-degree-x1] upsetplot/tests/test_upsetplot.py::test_process_data_series[cardinality-cardinality-x0] upsetplot/tests/test_upsetplot.py::test_process_data_series[cardinality-cardinality-x1] upsetplot/tests/test_upsetplot.py::test_process_data_series[cardinality-degree-x0] upsetplot/tests/test_upsetplot.py::test_process_data_series[cardinality-degree-x1] upsetplot/tests/test_upsetplot.py::test_subset_size_series[x0] upsetplot/tests/test_upsetplot.py::test_subset_size_series[x1] upsetplot/tests/test_upsetplot.py::test_sort_sets_by_deprecation[x0-None] upsetplot/tests/test_upsetplot.py::test_sort_sets_by_deprecation[x0-cardinality] upsetplot/tests/test_upsetplot.py::test_process_data_frame[None-cardinality-x0] upsetplot/tests/test_upsetplot.py::test_process_data_frame[None-degree-x0] upsetplot/tests/test_upsetplot.py::test_process_data_frame[cardinality-cardinality-x0] upsetplot/tests/test_upsetplot.py::test_process_data_frame[cardinality-degree-x0] upsetplot/tests/test_upsetplot.py::test_subset_size_frame[x0] upsetplot/tests/test_upsetplot.py::test_subset_size_frame[x1] upsetplot/tests/test_upsetplot.py::test_not_unique[None-cardinality] upsetplot/tests/test_upsetplot.py::test_not_unique[None-degree] upsetplot/tests/test_upsetplot.py::test_not_unique[cardinality-cardinality] upsetplot/tests/test_upsetplot.py::test_not_unique[cardinality-degree] upsetplot/tests/test_upsetplot.py::test_param_validation[kw0] upsetplot/tests/test_upsetplot.py::test_param_validation[kw1] upsetplot/tests/test_upsetplot.py::test_param_validation[kw2] upsetplot/tests/test_upsetplot.py::test_param_validation[kw3] upsetplot/tests/test_upsetplot.py::test_param_validation[kw4] upsetplot/tests/test_upsetplot.py::test_plot_smoke_test[kw0] upsetplot/tests/test_upsetplot.py::test_plot_smoke_test[kw1] upsetplot/tests/test_upsetplot.py::test_plot_smoke_test[kw2] upsetplot/tests/test_upsetplot.py::test_two_sets[set20-set10] upsetplot/tests/test_upsetplot.py::test_two_sets[set20-set11] upsetplot/tests/test_upsetplot.py::test_two_sets[set20-set12] upsetplot/tests/test_upsetplot.py::test_two_sets[set20-set13] upsetplot/tests/test_upsetplot.py::test_two_sets[set21-set10] upsetplot/tests/test_upsetplot.py::test_two_sets[set21-set11] upsetplot/tests/test_upsetplot.py::test_two_sets[set21-set12] upsetplot/tests/test_upsetplot.py::test_two_sets[set21-set13] upsetplot/tests/test_upsetplot.py::test_two_sets[set22-set10] upsetplot/tests/test_upsetplot.py::test_two_sets[set22-set11] upsetplot/tests/test_upsetplot.py::test_two_sets[set22-set12] upsetplot/tests/test_upsetplot.py::test_two_sets[set22-set13] upsetplot/tests/test_upsetplot.py::test_two_sets[set23-set10] upsetplot/tests/test_upsetplot.py::test_two_sets[set23-set11] upsetplot/tests/test_upsetplot.py::test_two_sets[set23-set12] upsetplot/tests/test_upsetplot.py::test_two_sets[set23-set13] upsetplot/tests/test_upsetplot.py::test_dataframe_raises upsetplot/tests/test_upsetplot.py::test_vertical upsetplot/tests/test_upsetplot.py::test_element_size upsetplot/tests/test_upsetplot.py::test_show_counts[horizontal] upsetplot/tests/test_upsetplot.py::test_show_counts[vertical] upsetplot/tests/test_upsetplot.py::test_add_catplot
upsetplot/plotting.py
upsetplot/plotting.py