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  • $\begingroup$ Thank you, it works! Can you explain me what #[[1,{2,3,4,5}]]&] does, please? $\endgroup$ Commented Aug 4, 2020 at 8:39
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    $\begingroup$ Sure. Part of the culture of Mathematica is to turn lots of stuff into punctuation characters. Stuff followed by & is a function, but we just use it and don't give it any name, look at the documentation reference.wolfram.com/language/ref/Function.html This function is going to have a single argument and that is indicated by # which will be any one of the items in your list. Then #[[1]] will extract the first part of your rule. And #[[1,{2,3,4,5}]] is going to extract the 2nd through 5th items out of that first part. SortBy uses this to extract the items to sort by. Is that enough? $\endgroup$ Commented Aug 4, 2020 at 8:53
  • $\begingroup$ Perhaps compare this f[r_]:=r[[1,{2,3,4,5}]]; SortBy[listofrules,f] to the #& version and see if that helps you a little. You can also search the help system for things like [[ and that will provide some explanation on how this is extracting the desired bits. $\endgroup$ Commented Aug 4, 2020 at 17:08