When using a text file (with a 'txt' or 'csv' extension), the input data must be a data frame with at least the columns "set", "map", "mkr", "phys" and "gen". If missing, an additional column "vld" (indicating if the marker is valid or not) is added with TRUE value by default. Column names must be in the first row and values must be separated by a space and each character string must be between double quotes (including column names). The rows which contains NA entries are removed. The "set" colum corresponds to the organism, "map" corresponds to chromosomes, "mkr" corresponds to markers, "phys" corresponds to physical position of markers, "gen" corresponds to genetic distances between each marker and "vld" corresponds to valid markers (this column is not mandatory).