title: How to add an observation category on scanpy based on another observation?
body: <p>I have a concatenated single-cell RNAseq anndata with</p>
  <pre><code>obs: 'Age', 'EPNsubtype', 'Region', 'Subclass', 
  'Taxonomy_group', 'Tissue', 'batch', 'pheno', 'sample', 
  'subtype', 'treatment', 'n_genes', 'percent_mito', 
  'n_counts', 'leiden'
  </code></pre>
  <p>And I want to create another obs <code>'Sex'</code> for the different 'samples'</p>
  <p>I know I can create a new obs with</p>
  <pre><code>adata.obs[&quot;sex&quot;] = &quot;female&quot;
  </code></pre>
  <p>but how would I do it for particular sample categories and not the entire set?</p>
  <p>Thanks!</p>