Comparison between observed abundanced and classifications plus the residuals of the classifications. Top panel: comparison between the observed abundances (star symbols where red/yellow symbols are elements that are included/excluded in our classification) and results (lines) of nearest-neighbour algorithm. Bottom panel: residuals of the classification (i.e. observed abundance minus predicted abundance for each element). This star is difficult to classify because the abundances in the first s-process peak are higher than predicted by the best-fit models.