Reading in only certain columns with DataSchema

Based on my current understanding from the [Data Schema concept page](https://review.docs.microsoft.com/en-us/nimbusml/concepts/schema?branch=smoke-test#dataschema-alterations), it seems that I can change the names/types of columns. However, can I read in only certain columns? I may have 10 columns but I only want to read 2 of them. Seeing all 10 in the schema can make things more complicated.