[MRG] add transformer for substraction of datetime variables

README.md

@@ -128,6 +128,7 @@ transforming parameters from the data and then transform it.
 
 ### Datetime
  * DatetimeFeatures
+ * DatetimeSubtraction
 
 ### Time Series
  * LagFeatures

docs/api_doc/datetime/DatetimeSubtraction.rst

@@ -0,0 +1,6 @@
+DatetimeSubtraction
+===================
+
+.. autoclass:: feature_engine.datetime.DatetimeSubtraction
+    :members:
+

docs/api_doc/datetime/index.rst

@@ -10,4 +10,5 @@ features from existing datetime or object-like data.
    :maxdepth: 1
 
    DatetimeFeatures
+   DatetimeSubtraction
 

docs/index.rst

@@ -164,6 +164,12 @@ Feature Creation:
 -  :doc:`api_doc/creation/RelativeFeatures`: combines variables with reference features
 -  :doc:`api_doc/creation/CyclicalFeatures`: creates variables using sine and cosine, suitable for cyclical features
 
+Datetime:
+---------
+
+- :doc:`api_doc/datetime/DatetimeFeatures`: extract features from datetime variables
+- :doc:`api_doc/datetime/DatetimeSubtraction`: computes subtractions between datetime variables
+
 Feature Selection:
 ------------------
 
@@ -180,11 +186,6 @@ Feature Selection:
 - :doc:`api_doc/selection/RecursiveFeatureElimination`: selects features recursively, by evaluating model performance
 - :doc:`api_doc/selection/RecursiveFeatureAddition`: selects features recursively, by evaluating model performance
 
-Datetime:
----------
-
-- :doc:`api_doc/datetime/DatetimeFeatures`: extract features from datetime variables
-
 Forecasting:
 ------------