Added identity_pal

closes #9

doc/changelog.rst

@@ -5,6 +5,8 @@ v0.4.5
 ------
 *(not-yet-released)*
 
+- Added :class:`~mizani.palettes.identity_pal`
+
 v0.4.4
 ------
 *(2017-12-13)*

mizani/palettes.py

@@ -25,6 +25,7 @@
 
 from .external import husl, xkcd_rgb, crayon_rgb
 from .bounds import rescale
+from .utils import identity
 
 
 __all__ = ['hls_palette', 'husl_palette', 'rescale_pal',
@@ -743,3 +744,24 @@ def cubehelix_palette(n):
         return [mcolors.rgb2hex(cubehelix_cmap(x)) for x in values]
 
     return cubehelix_palette
+
+
+def identity_pal():
+    """
+    Create palette that maps values onto themselves
+
+    Returns
+    -------
+    out : function
+        Palette function that takes a value or sequence of values
+        and returns the same values.
+
+    Examples
+    --------
+    >>> palette = identity_pal()
+    >>> palette(9)
+    9
+    >>> palette([2, 4, 6])
+    [2, 4, 6]
+    """
+    return identity

mizani/tests/test_palettes.py

@@ -9,7 +9,7 @@
                              area_pal, abs_area, grey_pal, hue_pal,
                              brewer_pal, gradient_n_pal, cmap_pal,
                              desaturate_pal, manual_pal, xkcd_palette,
-                             crayon_palette, cubehelix_pal)
+                             crayon_palette, cubehelix_pal, identity_pal)
 
 
 def test_hls_palette():
@@ -169,3 +169,14 @@ def test_cubehelix_pal():
     values = palette(5)
     assert len(values) == 5
     assert all(s[0] == '#' and len(s) == 7 for s in values)
+
+
+def test_identity_pal():
+    palette = identity_pal()
+
+    x = [1, 2, 3]
+    values = palette(x)
+    assert values == x
+
+    value = palette(10)
+    assert value == 10

mizani/utils.py

@@ -6,7 +6,9 @@
 
 __all__ = ['seq', 'fullseq', 'round_any', 'min_max', 'match',
            'precision', 'first_element', 'multitype_sort',
-           'is_close_to_int', 'same_log10_order_of_magnitude']
+           'is_close_to_int', 'same_log10_order_of_magnitude',
+           'identity'
+           ]
 
 DISCRETE_KINDS = 'ObUS'
 CONTINUOUS_KINDS = 'ifuc'
@@ -325,3 +327,10 @@ def same_log10_order_of_magnitude(rng, delta=0.045):
     """
     rng_adjusted = np.array(rng) + [-delta, +delta]
     return np.diff(rng_adjusted.astype(int))[0] == 0
+
+
+def identity(*args):
+    """
+    Return whatever is passed in
+    """
+    return args if len(args) > 1 else args[0]