Function parallelLayer

Reads a parallel as the parallel-coordinates plot it draws.

Measured, the series carries one row per observation and one dimension per variable -- ['dim0', 'dim1', 'dim2'] for a three-axis chart -- and the names those columns are drawn under live on the parallelAxis components rather than on the series:

parallelAxis: [{dim:0,name:'p'}, {dim:1,name:'q'}, {dim:2,name:'r'}]

so the axis names are read from there, in dim order, and fall back to the dimension's own name when the author wrote none (measured: name comes back as the empty string, not undefined).

Every point names its own axis in x, which is what ParallelTrace requires: it keys each axis's extent by name rather than by column position, so a value is pitched against its own variable's range even when an observation is short a reading (#1182).

It is read without an outline, and that is measured rather than conceded. The polylines are stroked, not filled, so the mark finder -- which pairs filled marks with data -- finds none at all: zero marks for a two-observation chart. Reading without one is what gauge, sankey and graph already do here.