Does this what you need?
\begin{filecontents*}{data.csv}
A;B
1.2.3;Some data
2.3.4,3.4.5;More data,Even more data
\end{filecontents*}
\documentclass[a4paper]{article}
% xparse/expl3 are included in more recent LaTeX2e-kernels
%\usepackage{expl3}
%\usepackage{xparse}
\usepackage{datatool}
\ExplSyntaxOn
\msg_new:nnn {MyStuff} {difflen} {two~comma~separated~lists~have~different~length}
\int_new:N \g_MyStuff_tempcntA
\int_new:N \g_MyStuff_tempcntB
\clist_new:N \g_MyStuff_clistA
\clist_new:N \g_MyStuff_clistB
\NewDocumentCommand\MergeDatabaseColumns{mmm}{
\DTLforeach{#1}{\A=A,\B=B}{
\int_gset:Nn \g_MyStuff_tempcntA {1}
\int_gset:Nn \g_MyStuff_tempcntB {0}
\clist_gset:No{\g_MyStuff_clistA}{\A}
\clist_gset:No{\g_MyStuff_clistB}{\B}
\int_compare:nNnTF {\clist_count:N \g_MyStuff_clistA} = {\clist_count:N \g_MyStuff_clistB} {
\int_gset:Nn \g_MyStuff_tempcntB {\clist_count:N \g_MyStuff_clistA}
\MyStuff_MergeListsloop:nn {#2}{#3}
}{
\msg_error:nn {MyStuff} {difflen}
}
}
}
\cs_new:Nn \MyStuff_MergeListsloop:nn {
% #1 space/column-separator
% #2 \newline/row-separator
\int_compare:nNnF {\g_MyStuff_tempcntB} < {\g_MyStuff_tempcntA} {
\clist_item:Nn \g_MyStuff_clistA {\g_MyStuff_tempcntA} #1
\clist_item:Nn \g_MyStuff_clistB {\g_MyStuff_tempcntA}
% Add the row-separator if not in last row of database.
% In last row of database add row-separator only if not at the last items of comma lists.
\DTLiflastrow{\int_compare:nNnF {\g_MyStuff_tempcntB} = {\g_MyStuff_tempcntA}{#2}}{#2}
\int_gincr:N \g_MyStuff_tempcntA
\MyStuff_MergeListsloop:nn{#1}{#2}
}
}
\ExplSyntaxOff
\DTLsetseparator{;}%
\DTLloaddb{data}{data.csv}
\begin{document}
\noindent \MergeDatabaseColumns{data}{ }{\newline}
\end{document}
Another example, providing two a little bit more generic routines:
\MergeDatabaseCellCommaLists{<database>}
{<name of database-field holding comma-list 1>}
{<name of database-field holding comma-list 2>}
{<Macro which processes arguments><Macro's arguments except last but one and last argument>,
the last but one argument being <item of comma-list 1>,
the last argument being <item of comma-list 2>,
In case the last list elements are reached, the switch
\ifLastListItem
is true.
In case the database's last row is reached, the switch
\ifLastRow
is true.
In case the database's last row's last list
elements are reached, the switch
\ifLastRowsLastListItem
is true.
The switches can be used in the definition and in the arguments
of <Macro which processes arguments>
}
and
\MergeCommaListsFromMacros{<Macro holding comma-list 1>; could come from a \DTLforeach's assignment-list}
{<Macro holding comma-list 2>; could come from a \DTLforeach's assignment-list}
{<Macro which processes arguments><Macro's arguments except last but one and last argument>,
the last but one argument being <item of comma-list 1>,
the last argument being <item of comma-list 2>,
In case the last list elements are reached, the switch
\ifLastListItem
is true.
In case of being inside a \DTLforeach-loop for iterating
rows of a database and the database's last row being
reached, the switch
\ifLastRow
is true.
In case of being inside a \DTLforeach-loop for iterating
rows of a database and the database's last row's last list
elements being reached, the switch
\ifLastRowsLastListItem
is true.
The switches can be used in the definition and in the arguments
of <Macro which processes arguments>
}
\begin{filecontents*}{data.csv}
A;B
1.2.3;Some data
2.3.4,3.4.5;More data,Even more data
\end{filecontents*}
\documentclass[a4paper]{article}
% xparse/expl3 are included in more recent kernels
%\usepackage{expl3}
%\usepackage{xparse}
\usepackage{datatool}
\makeatletter
\@ifdefinable\savedDTLiflastrow{\let\savedDTLiflastrow\DTLiflastrow}
\newcommand\AtIfInDTLLoop{%
\ifx\savedDTLiflastrow\DTLiflastrow
\expandafter\@secondoftwo\else\expandafter\@firstoftwo\fi
}
\makeatother
\ExplSyntaxOn
\newif\ifLastRowsLastListItem \global\LastRowsLastListItemfalse
\newif\ifLastListItem \global\LastListItemfalse
\newif\ifLastRow \global\LastRowfalse
\msg_new:nnn {MyStuff} {difflen} {two~comma~separated~lists~have~different~length}
\int_new:N \_MyStuff_tempcntA
\int_new:N \_MyStuff_tempcntB
\clist_new:N \_MyStuff_clistA
\clist_new:N \_MyStuff_clistB
\cs_new:Nn \_MyStuff_pushbehind:nnn {#3#1{#2}}
\cs_generate_variant:Nn \_MyStuff_pushbehind:nnn {nVn}
\cs_new:Nn \_MyStuff_passtwoargs:nnn {#1{#2}{#3}}
\cs_generate_variant:Nn \_MyStuff_passtwoargs:nnn {nxx}
%\MergeDatabaseCellCommaLists{<database>}
% {<name of database-field holding comma-list 1>}
% {<name of database-field holding comma-list 2>}
% {<Macro which processes arguments><Macro's arguments except last but one and last argument>,
% the last but one argument being <item of comma-list 1>,
% the last argument being <item of comma-list 2>,
% In case the last list elements are reached, the switch
% \ifLastListItem
% is true.
% In case the database's last row is reached, the switch
% \ifLastRow
% is true.
% In case the database's last row's last list
% elements are reached, the switch
% \ifLastRowsLastListItem
% is true.
% The switches can be used in the definition and in the arguments
% of <Macro which processes arguments>
% }
\NewDocumentCommand\MergeDatabaseCellCommaLists{mmmm}{
\DTLforeach{#1}{\A=#2,\B=#3}{\MergeCommaListsFromMacros{\A}{\B}{#4}}
}
%\MergeCommaListsFromMacros{<Macro holding comma-list 1>; could come from a \DTLforeach's assignment-list}
% {<Macro holding comma-list 2>; could come from a \DTLforeach's assignment-list}
% {<Macro which processes arguments><Macro's arguments except last but one and last argument>,
% the last but one argument being <item of comma-list 1>,
% the last argument being <item of comma-list 2>,
% In case the last list elements are reached, the switch
% \ifLastListItem
% is true.
% In case of being inside a \DTLforeach-loop for iterating
% rows of a database and the database's last row being
% reached, the switch
% \ifLastRow
% is true.
% In case of being inside a \DTLforeach-loop for iterating
% rows of a database and the database's last row's last list
% elements being reached, the switch
% \ifLastRowsLastListItem
% is true.
% The switches can be used in the definition and in the arguments
% of <Macro which processes arguments>
% }
\NewDocumentCommand\MergeCommaListsFromMacros{mmm}{
%
% \_MyStuff_pushbehind:nVn and \use_ii_i:nn are used to reset scratch-comma-lists
% \_MyStuff_clistA, \_MyStuff_clistB and \if-switches \ifLastListItem,
% \ifLastRow, \ifLastRowsLastListItem to the vales they had before starting
% the loop -- this way \MergeCommaListsFromMacros can be nested, i.e., the
% <Macro which processes arguments> can do another call to
% \MergeCommaListsFromMacros as long as you don't mess around with the
% \globaldefs-parameter.
%
\_MyStuff_pushbehind:nVn {\clist_set:Nn{\_MyStuff_clistA}}{\_MyStuff_clistA}{
\_MyStuff_pushbehind:nVn {\clist_set:Nn{\_MyStuff_clistB}}{\_MyStuff_clistB}{
\clist_set:No{\_MyStuff_clistA}{#1}
\clist_set:No{\_MyStuff_clistB}{#2}
\int_compare:nNnTF {\clist_count:N \_MyStuff_clistA} = {\clist_count:N \_MyStuff_clistB} {
\legacy_if:nTF{LastListItem}{
\use_ii_i:nn { \LastListItemtrue }% \legacy_if_set_true:n {LastListItem}
}{
\use_ii_i:nn {\LastListItemfalse }% \legacy_if_set_false:n {LastListItem}
}{
\legacy_if:nTF{LastRow}{
\use_ii_i:nn { \LastRowtrue }% \legacy_if_set_true:n {LastRow}
}{
\use_ii_i:nn { \LastRowfalse }% \legacy_if_set_false:n {LastRow}
}{
\legacy_if:nTF{LastRowsLastListItem}{
\use_ii_i:nn { \LastRowsLastListItemtrue }% \legacy_if_set_true:n {LastRowsLastListItem}
}{
\use_ii_i:nn { \LastRowsLastListItemfalse }% \legacy_if_set_false:n {LastRowsLastListItem}
}{
\_MyStuff_pushbehind:nVn {\int_set:Nn \_MyStuff_tempcntA}{\_MyStuff_tempcntA}{
\_MyStuff_pushbehind:nVn {\int_set:Nn \_MyStuff_tempcntB}{\_MyStuff_tempcntB}{
% \legacy_if_set_false:n {LastListItem}
\LastListItemfalse
%\legacy_if_set_false:n {LastRow}
\LastRowfalse
% \legacy_if_set_false:n {LastRowsLastListItem}
\LastRowsLastListItemfalse
\int_set:Nn \_MyStuff_tempcntA {1}
\int_set:Nn \_MyStuff_tempcntB {\clist_count:N \_MyStuff_clistA}
\_MyStuff_MergeListsloop:N {#3}
}
}
}
}
}
}{
\msg_error:nn {MyStuff} {difflen}
}
}
}
}
\cs_new:Nn \_MyStuff_MergeListsloop:N {
\int_compare:nNnF {\_MyStuff_tempcntB} < {\_MyStuff_tempcntA} {
\AtIfInDTLLoop{
\DTLiflastrow{
%\legacy_if_set_true:n {LastRow}
\LastRowtrue
}{}
}{}
\int_compare:nNnT {\_MyStuff_tempcntB} = {\_MyStuff_tempcntA}
{
%\legacy_if_set_true:n {LastListItem}
\LastListItemtrue
\legacy_if:nT {LastRow}
{
%\legacy_if_set_true:n {LastRowsLastListItem}
\LastRowsLastListItemtrue
}
}
\_MyStuff_passtwoargs:nxx {#1}
{\clist_item:Nn \_MyStuff_clistA {\_MyStuff_tempcntA}}
{\clist_item:Nn \_MyStuff_clistB {\_MyStuff_tempcntA}}
\int_incr:N \_MyStuff_tempcntA
\_MyStuff_MergeListsloop:N {#1}
}
}
\ExplSyntaxOff
\DTLsetseparator{;}%
\DTLloaddb{data}{data.csv}
\NewDocumentCommand\PrintElementsMerged{mmmm}{%
% #1 element-separator
% #2 row-separator
% #3 element from first list
% #4 element from second list
#3#1#4#2}%
\begin{document}
\noindent Lists come from database's data-fields A and B:
\noindent \MergeDatabaseCellCommaLists{data}{A}{B}{%
\PrintElementsMerged{ }{\ifLastRowsLastListItem\else\newline\fi}%
}
\bigskip
% Inside a \DTLforeach-Loop \ListA / \ListB could come from a \DTLforeach's assignment-list-argument.
% Instead of using \PrintMacroCommaListElementsMerged you can define and use whatsoever macro that
% processes two arguments, one of them being an element of the first list, the other being an element
% of the second list:
\noindent Lists come from macros \verb|\ListA| and \verb|\ListB|---the macros in turn could be due to
the assignment-list-argument of a \verb|\DTLforeach|-loop, but in this example are defined ``by hand'':
\def\ListA{1.2.3,2.3.4,3.4.5}
\def\ListB{Some data,More data,Even more data}
\noindent \MergeCommaListsFromMacros{\ListA}{\ListB}{%
\PrintElementsMerged{ }{\ifLastListItem\else\newline\fi}%
}
\end{document}
