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{AB1 => 100, NN => 200, XYZ => 400}
{AB1 => 100, XYZ => 400, MM => 300}

"AB1","NN","XYZ","MM"
"100","200","400",""
"100","","400","300"

AB1   NN       XYZ   MM
100   200      400   undef
100   undef    400   300