From 4a00ad79ddc508b16f15a58333475b0adb19ec6f Mon Sep 17 00:00:00 2001
From: DrPaprikaa <64958936+DrPaprikaa@users.noreply.github.com>
Date: Thu, 10 Sep 2020 21:25:23 +0200
Subject: [PATCH] Update _post_process() in core.py

@twopirllc,
In the case where an indicator returns a `df`, I added an option in `_post_process()`, via `kwargs`, to append only specific columns to the data. It goes like this :

```
CustomStrategy = ta.Strategy(
    name="MyStrat",
    ta=[
        {'kind':'bbands', 'params':(20,), 'col_numbers':(0,2)},
    ]
)
```

or alternatively : `ao = df.ta.bbands(append=True, col_numbers=(0,2))`

which can be usefull if the user needs only the upper and lower bbands for example.


Thanks,
DrPaprikaa
---
 pandas_ta/core.py | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/pandas_ta/core.py b/pandas_ta/core.py
index 4559635..aa0a48d 100644
--- a/pandas_ta/core.py
+++ b/pandas_ta/core.py
@@ -407,15 +407,18 @@ class AnalysisIndicators(BasePandasObject):
             return getattr(self,method)(*args, **kwargs)[0]
 
 
-    def _post_process(self, result, **kwargs) -> (Series, DataFrame):
+    def _post_process(self, result, **kwargs) -> (pd.Series, pd.DataFrame):
         """Applies any additional modifications to the DataFrame
         * Applies prefixes and/or suffixes
         * Appends the result to main DataFrame
         """
-        if not isinstance(result, (Series, DataFrame)):
+        if not isinstance(result, (pd.Series, pd.DataFrame)):
             print(f"[X] Oops! The result was not a Series or DataFrame.")
             return self._df
         else:
+            # Append only specific columns to the dataframe (via 'col_numbers':(0,1,3) for example)
+            result = result.iloc[:,[int(n) for n in kwargs['col_numbers']]] if isinstance(result, pd.DataFrame) and 'col_numbers' in kwargs and kwargs['col_numbers'] is not None else result
+            # Add prefix/suffix and append to the dataframe
             self._add_prefix_suffix(result=result, **kwargs)
             self._append(result=result, **kwargs)
         return result
@@ -1472,4 +1475,4 @@ class AnalysisIndicators(BasePandasObject):
         volume = self._get_column(kwargs.pop("volume", "volume"))
 
         result = vp(close=close, volume=volume, width=width, percent=percent, **kwargs)
-        return self._post_process(result, **kwargs)
\ No newline at end of file
+        return self._post_process(result, **kwargs)