1. A method for evaluating the class of a test datum in an original metric space, each datum belonging to at least one class grouping a plurality of data, the method comprising: graphical representation of the spatial organization of a set of learning data of the original space in a representation metric space, a conjoint membership level indicating if any two data from the learning set belong to the same class, the representation step including: projecting data from the learning set toward the representation metric space, the positions of the projections of the data in the representation space being those that minimize or maximize a function E, the function E depending on the differences between the weighted distances between the data from the learning set in the original space and the distances between their respective projections in the representation space, the weighting assigned in the function E to a distance between two data from the learning set depending on the fact that these two data belong to the same class, so as to preserve in the representation space the relative spatial organization of the classes; representation of the projections of the data from the learning set; relating the test datum to the projections of the data from the learning set, the most probable class of the test datum being the class of the projections of the data from the learning set related to the test datum.