  Modern visualization tools aim to allow data analysts to easily create
exploratory visualizations. When the input data layout conforms to the
visualization design, users can easily specify visualizations by mapping data
columns to visual channels of the design. However, when there is a mismatch
between data layout and the design, users need to spend significant effort on
data transformation.
  We propose Falx, a synthesis-powered visualization tool that allows users to
specify visualizations in a similarly simple way but without needing to worry
about data layout. In Falx, users specify visualizations using examples of how
concrete values in the input are mapped to visual channels, and Falx
automatically infers the visualization specification and transforms the data to
match the design. In a study with 33 data analysts on four visualization tasks
involving data transformation, we found that users can effectively adopt Falx
to create visualizations they otherwise cannot implement.
