Rocket spreads four decoded snapshot grids across the lab table: a star, a planet, a comet and a satellite streak.
"Hundreds of values each," he says. "Sky Sorter has to wade through all of them just for these four."
Raven draws a new table with only three columns. "What if each card became just three features?"
"Brightness, size and streak," Rocket says. "One row per card."
Nova lights up the first empty row. "That is a feature row," she says. "Stack the rows, and you have a feature table."
Raven fills in the first row. "Now the cards are ready for Sky Sorter."
A feature row is a row of values that describes one example. Each value is one feature.
A feature table stacks one row for every example. In Sky Sorter, each example is one snapshot card.
The feature table is another encoding. It keeps the features we chose and drops everything else.
The streak column holds yes or no. A computer could store that as 1 for yes and 0 for no.
| Card | Brightness (0 to 255) | Size (pixels wide) | Streak? | True label |
|---|---|---|---|---|
| P | 150 | 1 | no | star |
| Q | 220 | 5 | no | planet |
| R | 150 | 10 | no | comet |
| S | 120 | 6 | yes | satellite streak |
Every encoding keeps some information and drops the rest. The feature table drops the exact shape of each card.
For example, a fuzzy comet and a round planet could end up with the same size number on another day.
That is not a mistake yet. But it means Sky Sorter can only use what the features keep.
In later weeks, you will test whether these three features are enough.
| Statement | True or false? |
|---|---|
| A feature row describes one example with a few values. | ? |
| A feature table keeps every detail of every card. | ? |
| Yes and no could be stored as 1 and 0. | ? |
| Sky Sorter can use features that were dropped from the table. | ? |
Great table building. Tomorrow you will find encodings in everyday life.