add example one-liners for group management

README.md

@@ -113,9 +113,9 @@ python collect_forks.py \
         "group": "demo-group",
         "members": [
             {
-                "username": "studenta",
-                "name": "Student A",
-                "email": student.a@email.here
+                "username": "smcstudent",
+                "name": "Student McStudent",
+                "email": student.mcstudent@email.here
             }
         ],
         "commit": "0175894cf61fe820fdb84e5c52fc7ee0259a3c71",
@@ -162,6 +162,7 @@ After grading student assignments, the teacher may want to send student groups t
 
 <details>
 <summary> <b>Read more...</b> </summary>
+
 script: [teach\_utils/send\_feedback.py](teach_utils/send_feedback.py)
 
 **usage**:

docs/oneliners.md

+# Extracting group information with one liners
+
+This document lists a few one liners to extract useful group information from the JSON output of `collect_forks.json`.
+
+* Find the number of groups
+```sh
+$ jq 'length' forks.json
+
+20
+```
+
+* Get all groups with fewer than 3 students
+
+```sh
+$ jq '
+  .[] \
+  | {"group": .group, "size": (.members | length)} \
+  | select(.size < 3)' forks.json
+
+{
+  "group": "group-w",
+  "size": 1
+}
+```
+
+* Find all students present in multiple groups
+
+```sh
+$ jq '.[] | .members | map(.name) | .[]' forks.json \
+  | sort \
+  | uniq -dc
+
+2 "Student McStudent"
+```
+
+* Find students without group (using an external list of names)
+
+```sh
+# 1. Get the list of students in groups, sort it
+# 2. Sort the list of all enrolled students
+# 3. Find names which are in enrolled students, but not grouped students
+jq '.[] | .members | map(.name) | .[]' forks.json \
+  | sort \
+  | uniq -d \
+  | sed 's/^ *//' \
+  | comm -23 <( sort enrolled_students.txt) -
+"John Smith"
+```
\ No newline at end of file