title: How to properly use functions from other packages in a R package
body: <p>I am a bit confused about this. I have an R package that has a small function (not a mayor part of the package) in which the <code>principal</code> function of the <code>psych</code> package is called. How do I correctly specify this in DESCRIPTION and NAMESPACE?</p>
  
  <p>Setting <code>Depends: psych</code> in DESCRIPTION makes sure the psych package is loaded every time my package is loaded. This works, but it seems redundant for such a small part of my package.</p>
  
  <p>Setting <code>Suggests: psych</code> and entering a <code>require("psych")</code> in the function is what I do now, however this does not work if <code>psych</code> is not installed, and seems to be the wrong way of doing this (writing R extensions says that suggest is meant mainly for examples).</p>
  
  <p>I think I need to import the function. I tried setting <code>Imports: psych</code> in DESCRIPTION and <code>importFrom(psych,"principal")</code> in NAMESPACE. This works, but on a computer that does not has psych installed it gives an error when loading my package.</p>