Explode all the attributes and ignore all the numeric and FME fields.
" POSITION="-64 -235.75043750437504" TOP_LEFT="-64 -235.75043750437504" BOTTOM_RIGHT="743.75743757437567 -422.0020000200002" BOUNDING_RECT="-64 -235.75043750437504 807.75743757437567 186.25156251562515" ORDER="500000000000120" FOLLOW_ANCHOR="true" INFO_NODE="false" CUSTOM_USER_COLOR="false" COLOUR="1,1,0.95686274509803926,0.78431372549019607" SIZE_POLICY="10" ANCHORED_NODE="11">Select the values that have the max length, and pick the first one
" POSITION="2368 -320" TOP_LEFT="2368 -320" BOTTOM_RIGHT="3228.2835628356283 -462.50112501125011" BOUNDING_RECT="2368 -320 860.28356283562835 142.50112501125011" ORDER="499999999999999" FOLLOW_ANCHOR="true" INFO_NODE="false" CUSTOM_USER_COLOR="false" COLOUR="1,1,0.95686274509803926,0.78431372549019607" SIZE_POLICY="10" ANCHORED_NODE="18">Group by _attr_name,
and calculate the max length
" POSITION="1792 -576" TOP_LEFT="1792 -576" BOTTOM_RIGHT="2373.2558125581254 -718.50112501125011" BOUNDING_RECT="1792 -576 581.2558125581254 142.50112501125011" ORDER="500000000000130" FOLLOW_ANCHOR="true" INFO_NODE="false" CUSTOM_USER_COLOR="false" COLOUR="1,1,0.95686274509803926,0.78431372549019607" SIZE_POLICY="10" ANCHORED_NODE="4">Sort the list of attributes alphatically or longest first
" POSITION="3392 -320" TOP_LEFT="3392 -320" BOTTOM_RIGHT="3947.0407504075038 -462.50112501125011" BOUNDING_RECT="3392 -320 555.04075040750377 142.50112501125011" ORDER="499999999999998" FOLLOW_ANCHOR="true" INFO_NODE="false" CUSTOM_USER_COLOR="false" COLOUR="1,1,0.95686274509803926,0.78431372549019607" SIZE_POLICY="10" ANCHORED_NODE="26">NB: Selecting "Type Is STRING" doesn't work, as it selects all attributes!!
" POSITION="-64 -1536" TOP_LEFT="-64 -1536" BOTTOM_RIGHT="817.25831258312587 -1535" BOUNDING_RECT="-64 -1536 881.25831258312587 -1" ORDER="499999999999997" FOLLOW_ANCHOR="true" INFO_NODE="false" CUSTOM_USER_COLOR="false" COLOUR="1,1,0.95686274509803926,0.78431372549019607" SIZE_POLICY="10" ANCHORED_NODE="16">