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ENH: Styler.highlight_null can accepts subset argument #31350

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Merged
merged 6 commits into from
Mar 10, 2020
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ENH: Styler.highlight_null can accepts subset argument #31350

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ENH: `Styler.highlight_null` can accepts `subset` argument
immaxchen Jan 27, 2020
e22a656
mentioned default color in docstring
immaxchen Jan 28, 2020
2f1ea73
modify docstring
immaxchen Mar 1, 2020
1075f0b
resolve whatsnew conflict
immaxchen Mar 1, 2020
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add annotation
immaxchen Mar 5, 2020
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Merge remote-tracking branch 'upstream/master' into ENH-highlight_nul…
immaxchen Mar 10, 2020
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v1.1.0.rst
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Expand Up @@ -42,6 +42,7 @@ Other enhancements
^^^^^^^^^^^^^^^^^^

- :class:`Styler` may now render CSS more efficiently where multiple cells have the same styling (:issue:`30876`)
- :meth:`Styler.highlight_null` now accepts ``subset`` argument (:issue:`31345`)
-
-

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10 changes: 7 additions & 3 deletions pandas/io/formats/style.py
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Expand Up @@ -1006,19 +1006,23 @@ def hide_columns(self, subset) -> "Styler":
def _highlight_null(v, null_color: str) -> str:
return f"background-color: {null_color}" if pd.isna(v) else ""

def highlight_null(self, null_color: str = "red") -> "Styler":
def highlight_null(self, null_color: str = "red", subset=None) -> "Styler":
"""
Shade the background ``null_color`` for missing values.

Parameters
----------
null_color : str
null_color : str, default 'red'
subset : IndexSlice, default None
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This isn't an IndexSlice right? Just a label or list of labels?

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It is an IndexSlice, since it calls self.applymap and applymap uses IndexSlice.

< code >

pandas/pandas/io/formats/style.py

Lines 729 to 736 in e22a656

def _applymap(self, func: Callable, subset=None, **kwargs) -> "Styler":
func = partial(func, **kwargs) # applymap doesn't take kwargs?
if subset is None:
subset = pd.IndexSlice[:]
subset = _non_reducing_slice(subset)
result = self.data.loc[subset].applymap(func)
self._update_ctx(result)
return self

< proof >

image

< the doc >

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The test case here though is not for an IndexSlice rather a list of labels. I think for a natural API should go with Label / Sequence of Labels as mentioned above

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It can take Label / Sequence of Labels as well, just like other Styler built-in methods.

image

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Can you update this to label or list of labels?

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sure.

A valid slice for ``data`` to limit the style application to.

.. versionadded:: 1.1.0

Returns
-------
self : Styler
"""
self.applymap(self._highlight_null, null_color=null_color)
self.applymap(self._highlight_null, null_color=null_color, subset=subset)
return self

def background_gradient(
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17 changes: 17 additions & 0 deletions pandas/tests/io/formats/test_style.py
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Expand Up @@ -1091,6 +1091,23 @@ def test_highlight_null(self, null_color="red"):
expected = {(0, 0): [""], (1, 0): ["background-color: red"]}
assert result == expected

def test_highlight_null_subset(self):
# GH 31345
df = pd.DataFrame({"A": [0, np.nan], "B": [0, np.nan]})
result = (
df.style.highlight_null(null_color="red", subset=["A"])
.highlight_null(null_color="green", subset=["B"])
._compute()
.ctx
)
expected = {
(0, 0): [""],
(1, 0): ["background-color: red"],
(0, 1): [""],
(1, 1): ["background-color: green"],
}
assert result == expected

def test_nonunique_raises(self):
df = pd.DataFrame([[1, 2]], columns=["A", "A"])
with pytest.raises(ValueError):
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