BUG: interpolation with duplicate index values fails (pandas-dev#42585)

ben · ben · commit 6009daa29acd · 2021-08-14T09:56:28.000-07:00
diff --git a/pandas/core/missing.py b/pandas/core/missing.py
@@ -430,7 +430,7 @@ def _interpolate_1d(
     if method in NP_METHODS:
         # np.interp requires sorted X values, #21037
 
-        indexer = np.argsort(indices[valid])
+        indexer = np.argsort(indices[valid], kind="stable")
         result[invalid] = np.interp(
             indices[invalid], indices[valid][indexer], yvalues[valid][indexer]
         )

Original file line number	Diff line number	Diff line change
`@@ -430,7 +430,7 @@ def _interpolate_1d(`
`430`	`430`	`if method in NP_METHODS:`
`431`	`431`	`# np.interp requires sorted X values, #21037`
`432`	`432`
`433`		`- indexer = np.argsort(indices[valid])`
	`433`	`+ indexer = np.argsort(indices[valid], kind="stable")`
`434`	`434`	`result[invalid] = np.interp(`
`435`	`435`	`indices[invalid], indices[valid][indexer], yvalues[valid][indexer]`
`436`	`436`	`)`