Customized list of elements using etoolbox

When you type \the#2 you have an already formed token, so this will not be merged into a single command name such as \thelistAcounter. You have to build the name yourself:

\documentclass{article} \usepackage{etoolbox} \newcounter{listAcounter} \newcommand\addToList[3]{% \stepcounter{#2}% \csdef{#1\csuse{the#2}}{#3} } \newcommand\getFromList[2]{% \csuse{#1#2}% } \begin{document} \addToList{listA}{listAcounter}{one} \addToList{listA}{listAcounter}{two} \addToList{listA}{listAcounter}{three} This is element 2 from list A: \getFromList{listA}{2}. \end{document} 

Note the % after \csuse{#1#2}.

An easier implementation with expl3, that avoids defining a counter.

\documentclass{article} \usepackage{xparse} \ExplSyntaxOn \NewDocumentCommand{\newList}{m} { \seq_new:c { l_kees_list_#1_seq } } \NewDocumentCommand{\addToList}{mm} { \seq_put_right:cn { l_kees_list_#1_seq } { #2 } } \NewDocumentCommand{\getFromList}{mm} { \seq_item:cn { l_kees_list_#1_seq } { #2 } } \ExplSyntaxOff \begin{document} \newList{listA} \addToList{listA}{one} \addToList{listA}{two} \addToList{listA}{three} This is element 2 from list A: \getFromList{listA}{2}. \end{document}