Migrate `export_informative` function

Issue:
https://github.com/genenetwork/gn-gemtext-threads/blob/main/topics/gn1-migration-to-gn2/partial-correlations.gmi

* gn3/partial_correlations.py: Implement a mostly, bug-compatible
  `export_informative` function as part of migrating the partial correlations
  feature over to GN3 from GN1
* tests/unit/test_partial_correlations.py: Implement tests to ensure the code
  work in a similar manner as that one in GN1.

1 files changed, 32 insertions, 0 deletions

diff --git a/gn3/partial_correlations.py b/gn3/partial_correlations.py
new file mode 100644
index 0000000..8c37886
--- /dev/null
+++ b/gn3/partial_correlations.py
@@ -0,0 +1,32 @@
+"""
+This module deals with partial correlations.
+
+It is an attempt to migrate over the partial correlations feature from
+GeneNetwork1.
+"""
+
+from functools import reduce
+
+def export_informative(trait_data: dict, inc_var: bool = False) -> tuple:
+    """
+    Export informative strain
+
+    This is a migration of the `exportInformative` function in
+    web/webqtl/base/webqtlTrait.py module in GeneNetwork1.
+
+    There is a chance that the original implementation has a bug, especially
+    dealing with the `inc_var` value. It the `inc_var` value is meant to control
+    the inclusion of the `variance` value, then the current implementation, and
+    that one in GN1 have a bug.
+    """
+    def __exporter__(acc, data_item):
+        if not inc_var or data_item["variance"] is not None:
+            return (
+                acc[0] + (data_item["sample_name"],),
+                acc[1] + (data_item["value"],),
+                acc[2] + (data_item["variance"],))
+        return acc
+    return reduce(
+        __exporter__,
+        filter(lambda td: td["value"] is not None, trait_data["data"].values()),
+        (tuple(), tuple(), tuple()))