title: How do I assign grouped values (per-subject) from one df to another df that's grouped by trial (e.g. repeated rows for each subject)
body: <p>I am using R.</p>
  <p>I have two dfs, A and B.</p>
  <p>A is grouped by trial, so contains numerous observations for each subject (e.g. reaction times per trial).</p>
  <p>B is grouped by subject, so contains just one observation per subject (e.g. self-reported individual difference measures).</p>
  <p>I want to transfer the B values so they repeat per participant across trials in A. There are numerous variables I wish to transfer from B to A, so I'm looking for an elegant solution.</p>