Opens separate outliner window and filters materials

outliner_materials_only.py

def RShowMatsOutliner():

    #check if window exists
    if (cmds.window("R_MaterialLister", exists=True)):
        cmds.deleteUI("R_MaterialLister")
    else:
        # window and mainLayout
        window = cmds.window("R_MaterialLister", title="Material Lister")

        form = cmds.formLayout(numberOfDivisions=100, width=100)
        panel = cmds.outlinerPanel()
        outliner = cmds.outlinerPanel(panel, query=True,outlinerEditor=True)
        cmds.outlinerEditor( outliner, edit=True, mainListConnection='worldList', selectionConnection='modelList', showShapes=False, showAttributes=False, showConnected=False, showAnimCurvesOnly=False, autoExpand=False, showDagOnly=False, ignoreDagHierarchy=False, expandConnections=False, showNamespace=True, showCompounds=True, showNumericAttrsOnly=False, highlightActive=True, autoSelectNewObjects=False, doNotSelectNewObjects=False, transmitFilters=False, showSetMembers=True, setFilter='defaultSetFilter' )

        cmds.formLayout( form, edit=True, attachForm=[(panel, 'top', -48), (panel, 'left', 0), (panel, 'right', 0), (panel, 'bottom', 0)] )

        cmds.showWindow(window)

        #set material filter
        sel_mem = cmds.ls(sl=True)
        sceneshaders = cmds.ls(mat=True)
        cmds.select(sceneshaders)
        mel.eval('filterUIFilterSelection %s "filler"' %panel)
        cmds.select(sel_mem)