多层数据注入同一个图层源时，要批量删除某一种要素

//添加要素 
for (var i = 0; i < obj.length; i++) {
            var coodinate = [Number(obj[i].lon), Number(obj[i].lat)];
            var point = new ol.geom.Point(coodinate);
            //根据坐标生成要素点
            var feature = new ol.Feature({
                geometry: point,
                tablename: tablename,
                featureId: obj[i].id
            });
            //设置样式
            feature.setStyle(new ol.style.Style({
                image: new ol.style.Icon({
                    anchor: [0.5, 30],
                    anchorXUnits: ‘fraction‘,
                    anchorYUnits: ‘pixels‘,
                    src: icons[4]
                }),
                text: new ol.style.Text({
                    text: obj[i].name,
                    font: ‘700 12px 微软雅黑‘,
                    fill: new ol.style.Fill({
                        color: "#000"
                    }),
                    stroke: new ol.style.Stroke({
                        color: "rgb(253,252,252)",
                        width: 0.5
                    }),
                    offsetY: -35,
                })
            }));
            features.push(feature);

//将各类要素同时加入到featureList

featureList.push(feature) 

}
//遍历删除要素

buliding_source.clear();
        for (var i = 0; i < featureList.length; i++) {
            if (featureList[i].N.tablename == tablename) {
                featureList.splice(i, 1);
                i--;
            }
        }
        buliding_source.addFeatures(featureList);