[ENH] Rename Feature Constructor to Formula (#6549)

* Rename Feature Constructor to Formula

* Update widget.json

* feature-constructor2-stamped.png - resize and index

* Formula documentation: Minor changes

* index.rst - fix reference to formula

* move accidentally displaced formula.md

---------

Co-authored-by: PrimozGodec <p.godec9@gmail.com>

Orange/widgets/data/owfeatureconstructor.py

@@ -509,12 +509,12 @@ def is_valid_item(self, setting, item, attrs, metas):
 
 
 class OWFeatureConstructor(OWWidget, ConcurrentWidgetMixin):
-    name = "Feature Constructor"
+    name = "Formula"
     description = "Construct new features (data columns) from a set of " \
                   "existing features in the input dataset."
     category = "Transform"
     icon = "icons/FeatureConstructor.svg"
-    keywords = "feature constructor, function, lambda"
+    keywords = "feature constructor, function, lambda, calculation"
     priority = 2240
 
     class Inputs:

doc/visual-programming/source/index.rst

@@ -48,7 +48,7 @@ Data
    widgets/data/paintdata
    widgets/data/pivot
    widgets/data/pythonscript
-   widgets/data/featureconstructor
+   widgets/data/formula
    widgets/data/editdomain
    widgets/data/impute
    widgets/data/mergedata

doc/visual-programming/source/widgets/data/formula.md

@@ -0,0 +1,58 @@
+Formula
+=======
+
+Add new features to your dataset.
+
+**Inputs**
+
+- Data: input dataset
+
+**Outputs**
+
+- Data: dataset with additional features
+
+**Formula** allows computing new columns by combining the existing ones with a user-defined expression. The resulting column can be categorical, numerical or textual.
+
+For numeric variables, it sufices to provide a name and an expression.
+
+![](images/feature-constructor1-stamped.png)
+
+1. List of constructed variables
+2. Add or remove variables
+3. New feature name
+4. Expression in Python
+5. Select a feature
+6. Select a function
+7. Produce a report
+8. Press *Send* to communicate changes
+
+The following example shows construction of a categorical variable: its value is "lower" is "sepal length" is below 6, "mid" if it is at least 6 but below 7, and "higher" otherwise. Note that spaces need to be replaced by underscores (`sepal_length`).
+
+![](images/feature-constructor2-stamped.png)
+
+1. List of variable definitions
+2. Add or remove variables
+3. New feature name
+4. Expression in Python
+5. If checked, the feature is put among meta attributes
+6. Select a feature to use in expression
+7. Select a function to use in expression
+8. Optional list of values, used to define their order
+9. Press *Send* to compute and output data
+
+Hints
+-----
+
+If you are unfamiliar with Python math language, here's a quick introduction.
+
+Expressions can use the following operators:
+- `+`, `-`, `*`, `/`: addition, subtraction, multiplication, division
+- `//`: integer division
+- `%`: remainder after integer division
+- `**`: exponentiation (for square root square by 0.5)
+- `<`, `>`, `<=`, `>=` less than, greater than, less or equal, greater or equal
+- `==` equal
+- `!=` not equal
+- if-else: *value* `if` *condition* else *other-value* (see the above example
+
+See more [here](http://www.tutorialspoint.com/python/python_basic_operators.htm).

doc/widgets.json

@@ -345,14 +345,15 @@
     ]
    },
    {
-    "text": "Feature Constructor",
-    "doc": "visual-programming/source/widgets/data/featureconstructor.md",
+    "text": "Formula",
+    "doc": "visual-programming/source/widgets/data/formula.md",
     "icon": "../Orange/widgets/data/icons/FeatureConstructor.svg",
     "background": "#FF9D5E",
     "keywords": [
      "feature constructor",
      "function",
-     "lambda"
+     "lambda",
+     "calculation"
     ]
    },
    {