# Selection in resemblance matrices

Looking ahead to Section [5](https://learninghub.primer-e.com/books/primer-v7-user-manual-tutorial/chapter/5-resemblance-similarities-dissimilarities-and-distances), when the active window is a (triangular) resemblance matrix, selection can take place just as for a (rectangular) datasheet, by **Select>Highlighted** or **Select>Samples>**(•Sample numbers) or (•Factor levels). Another option is provided in that case: selection of only the rows and columns containing at least one value above or below a specified threshold by, for example, **Select>Samples>**(•Values><ins>0.95</ins>), or selecting only rows and columns containing at least one <code style ="color : green">Undefined!</code>  resemblance entry, by **Select>Samples>**(•Undefined values). These are mainly used for picking out, in the first case, collinear environmental variables from a large correlation matrix (values > 0.95 or <–0.95 say), Section [13](https://learninghub.primer-e.com/books/primer-v7-user-manual-tutorial/chapter/13-linking-assemblage-to-environment-best-bio-env-linktree). In the second case, this might more easily identify similarities that are undefined because neither sample contains any species at all, in cases where the similarity measure (such as Bray-Curtis) treats such samples as uninformative, Section [5](https://learninghub.primer-e.com/books/primer-v7-user-manual-tutorial/chapter/5-resemblance-similarities-dissimilarities-and-distances).