Is there a way in Altair to use one shape for all the elements in a dataframe but the last? I have data columns and a category column. I'd like all but one of the categories to plot with a circle and one category to plot with a diamond.

I understand how to set shape and color ranges, but I don't understand how to set them conditionally based on the data, just the order and values of the shapes/colors

This is a simplified example:

```py

myData = {'category':['Cat 1','Cat 2','Cat 3'], 
          'valueX':['10','20','30'], 
          'valueY':['10','20','30']}

df = pd.DataFrame(data=myData)

alt.Chart(df).mark_point().encode(
  x = 'valueX',
  y = 'valueY',
  shape = alt.Shape('category', scale=alt.Scale(range=['circle','diamond']))
)

```

This just alternates between the circle and diamond. How do I have my first two categories use the circle and 'Cat 3' use the diamond?