lidavidm commented on code in PR #34267:
URL: https://github.com/apache/arrow/pull/34267#discussion_r1118931541
##########
cpp/src/arrow/compute/exec/options.h:
##########
@@ -582,6 +582,94 @@ class ARROW_EXPORT TableSinkNodeOptions : public
ExecNodeOptions {
bool sequence_output = false;
};
+struct ARROW_EXPORT PivotLongerRowTemplate {
+ PivotLongerRowTemplate(std::vector<std::string> feature_values,
+ std::vector<std::optional<FieldRef>>
measurement_values)
+ : feature_values(std::move(feature_values)),
+ measurement_values(std::move(measurement_values)) {}
+ /// A (typically unique) set of feature values for the template, usually
derived from a
+ /// column name
+ ///
+ /// These will be used to populate the feature columns
+ std::vector<std::string> feature_values;
+ /// The fields containing the measurements to use for this row
+ ///
+ /// These will be used to populate the measurement columns. If nullopt then
nulls
+ /// will be inserted for the given value.
+ std::vector<std::optional<FieldRef>> measurement_values;
+};
+
+/// \brief Reshape a table by turning some columns into additional rows
+///
+/// This operation is sometimes also referred to as UNPIVOT
+///
+/// This is typically done when there are multiple observations in each row in
order to
+/// transform to a table containing a single observation per row.
+///
+/// For example:
+///
+/// | time | left_temp | right_temp |
+/// | ---- | --------- | ---------- |
+/// | 1 | 10 | 20 |
+/// | 2 | 15 | 18 |
+///
+/// The above table contains two observations per row. There is an implicit
feature
+/// "location" (left vs right) and a measurement "temp". What we really want
is:
+///
+/// | time | location | temp |
+/// | 1 | left | 10 |
Review Comment:
```suggestion
/// | time | location | temp |
/// | ---- | -------- | --- |
/// | 1 | left | 10 |
```
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