---------</span>
keys &lt;-<span class="st"> </span><span class="kw">read.csv</span>(<span class="st">&quot;data/raw/key_file.csv&quot;</span>)

<span class="kw">names</span>(t0)[<span class="dv">1</span>] &lt;-<span class="st"> &quot;Survey_ID&quot;</span>
t0 &lt;-<span class="st"> </span><span class="kw">merge</span>(t0, keys)

<span class="co"># only keep variables of interest ----------------------------</span>
<span class="co"># (gender, age, phq item scores)</span>
t0 &lt;-<span class="st"> </span>t0[