step,rule,n_before,n_after,n_removed,rationale
0_read,all data lines in sales.csv (excluding header),1200,1200,0,starting count
1_structure,exactly 5 CSV fields and sale_id matches S+5 digits,1200,1164,36,corrupted/garbled lines whose fields cannot be read unambiguously; not reconstructed
2_fields,"valid ISO date, integer price (CSV-quoted thousands separators allowed), area>0, non-empty municipality",1164,1164,0,fields must be readable unambiguously
3_dedup,unique sale_id,1164,1164,0,sale_id must be unique
4_final,analytic dataset,1164,1164,0,n_analysed