Very simply, what is the best way to understand what the trace feature represents (which adds a line to the middle of each column when drawing a heatmap) of heatmap.2 in R? There's practically nothing online about this (yet).
character string indicating whether a solid "trace" line should be drawn across 'row's or down 'column's, 'both' or 'none'. The distance of the line from the center of each color-cell is proportional to the size of the measurement. Defaults to 'column'.