Revert "[BUG]: Isin converted floats unnecessarily to int causing rounding issues"

This reverts commit addfd75

Author: phofl

pandas/core/algorithms.py

@@ -19,7 +19,6 @@
     construct_1d_object_array_from_listlike,
     infer_dtype_from_array,
     maybe_promote,
-    maybe_upcast,
 )
 from pandas.core.dtypes.common import (
     ensure_float64,
@@ -450,13 +449,6 @@ def isin(comps: AnyArrayLike, values: AnyArrayLike) -> np.ndarray:
         return np.zeros(comps.shape, dtype=bool)
 
     comps, dtype = _ensure_data(comps)
-    if is_numeric_dtype(comps):
-        try:
-            # Try finding a dtype which would not change our values
-            values, _ = maybe_upcast(values, dtype=dtype)
-            dtype = values.dtype
-        except (ValueError, TypeError):
-            pass
     values, _ = _ensure_data(values, dtype=dtype)
 
     f = htable.ismember_object
@@ -472,7 +464,7 @@ def isin(comps: AnyArrayLike, values: AnyArrayLike) -> np.ndarray:
             f = lambda c, v: np.logical_or(np.in1d(c, v), np.isnan(c))
         else:
             f = np.in1d
-    elif is_integer_dtype(comps.dtype) and is_integer_dtype(values):
+    elif is_integer_dtype(comps.dtype):
         try:
             values = values.astype("int64", copy=False)
             comps = comps.astype("int64", copy=False)
@@ -481,7 +473,7 @@ def isin(comps: AnyArrayLike, values: AnyArrayLike) -> np.ndarray:
             values = values.astype(object)
             comps = comps.astype(object)
 
-    elif is_numeric_dtype(comps.dtype) or is_numeric_dtype(values):
+    elif is_float_dtype(comps.dtype):
         try:
             values = values.astype("float64", copy=False)
             comps = comps.astype("float64", copy=False)