add documentation for unique df command

DataFrames.md

@@ -198,23 +198,23 @@ shape: (5356, 6)
 │ ---                     ┆ ---   ┆ ---    ┆ ---    ┆ ---   ┆ ---    │
 │ str                     ┆ str   ┆ f64    ┆ f64    ┆ f64   ┆ f64    │
 ╞═════════════════════════╪═══════╪════════╪════════╪═══════╪════════╡
-│ images/000000000581.jpg ┆ dog   ┆ 49.37  ┆ 67.79  ┆ 74.29 ┆ 116.08 │
+│ images/000000000581.jpg ┆ dog   ┆ 49.37  ┆ 67.79  ┆ 74.29 ┆ 216.08 │
 ├╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┤
-│ images/000000001360.jpg ┆ dog   ┆ 101.56 ┆ 178.2  ┆ 35.22 ┆ 38.34  │
+│ images/000000001360.jpg ┆ dog   ┆ 101.56 ┆ 178.2  ┆ 35.22 ┆ 238.34 │
 ├╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┤
-│ images/000000362567.jpg ┆ dog   ┆ 90.96  ┆ 36.65  ┆ 86.2  ┆ 185.08 │
+│ images/000000362567.jpg ┆ dog   ┆ 90.96  ┆ 36.65  ┆ 86.2  ┆ 285.08 │
 ├╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┤
-│ images/000000201969.jpg ┆ dog   ┆ 167.24 ┆ 73.99  ┆ 37.0  ┆ 64.94  │
+│ images/000000201969.jpg ┆ dog   ┆ 167.24 ┆ 73.99  ┆ 37.0  ┆ 264.94 │
 ├╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┤
 │ ...                     ┆ ...   ┆ ...    ┆ ...    ┆ ...   ┆ ...    │
 ├╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┤
-│ images/000000237419.jpg ┆ dog   ┆ 49.64  ┆ 104.53 ┆ 31.31 ┆ 48.88  │
+│ images/000000237419.jpg ┆ dog   ┆ 49.64  ┆ 104.53 ┆ 31.31 ┆ 248.88 │
 ├╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┤
-│ images/000000314708.jpg ┆ dog   ┆ 47.17  ┆ 138.18 ┆ 54.72 ┆ 59.55  │
+│ images/000000314708.jpg ┆ dog   ┆ 47.17  ┆ 138.18 ┆ 54.72 ┆ 359.55 │
 ├╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┤
-│ images/000000257301.jpg ┆ dog   ┆ 84.85  ┆ 161.09 ┆ 33.1  ┆ 51.26  │
+│ images/000000257301.jpg ┆ dog   ┆ 84.85  ┆ 161.09 ┆ 33.1  ┆ 251.26 │
 ├╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌┤
-│ images/000000130399.jpg ┆ dog   ┆ 51.63  ┆ 157.14 ┆ 53.13 ┆ 29.75  │
+│ images/000000130399.jpg ┆ dog   ┆ 51.63  ┆ 157.14 ┆ 53.13 ┆ 229.75 │
 └─────────────────────────┴───────┴────────┴────────┴───────┴────────┘
 ```
 
@@ -379,6 +379,15 @@ Here is a list of supported output aggregation functions:
 * `head` first 5 values of group
 * `tail` last 5 values of the group
 
+## Unique
+
+Oxen can efficiently compute all the unique values given a column name, or comma separated list of column names.
+
+```
+$ oxen df annotations/train.csv --unique "file"
+$ oxen df annotations/train.csv -u "file,label"
+```
+
 ## Sort
 
 Sorting can be achieved with the `sort` flag. For example you may want to find the largest bounding boxes by sorting on the height column.