Please try this, and let me know if it helps.
[{"id":"f17abf82.120ce8","type":"join","z":"928d9b65.5f22a","name":"","mode":"custom","build":"object","property":"payload","propertyType":"msg","key":"topic","joiner":"","joinerType":"str","accumulate":false,"timeout":"","count":"3","reduceRight":false,"reduceExp":"","reduceInit":"","reduceInitType":"","reduceFixup":"","x":830,"y":160,"wires":[["6676789b.2648a8"]]},{"id":"4cef14bf.99f06c","type":"change","z":"928d9b65.5f22a","name":"set topic 1","rules":[{"t":"set","p":"topic","pt":"msg","to":"a","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":610,"y":120,"wires":[["f17abf82.120ce8"]]},{"id":"f1b62f14.58da2","type":"change","z":"928d9b65.5f22a","name":"set topic 2","rules":[{"t":"set","p":"topic","pt":"msg","to":"b","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":610,"y":160,"wires":[["f17abf82.120ce8"]]},{"id":"452690cc.e4b968","type":"change","z":"928d9b65.5f22a","name":"set topic 3","rules":[{"t":"set","p":"topic","pt":"msg","to":"c","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":610,"y":200,"wires":[["f17abf82.120ce8"]]},{"id":"e0859aba.9c11b8","type":"inject","z":"928d9b65.5f22a","name":"","topic":"","payload":"1","payloadType":"num","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":410,"y":120,"wires":[["4cef14bf.99f06c"]]},{"id":"f32c41ac.b54678","type":"inject","z":"928d9b65.5f22a","name":"","topic":"","payload":"2","payloadType":"num","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":410,"y":160,"wires":[["f1b62f14.58da2"]]},{"id":"717ee388.87a1ac","type":"inject","z":"928d9b65.5f22a","name":"","topic":"","payload":"3","payloadType":"num","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":410,"y":200,"wires":[["452690cc.e4b968"]]},{"id":"6676789b.2648a8","type":"function","z":"928d9b65.5f22a","name":"list","func":"a = msg.payload.a\nb = msg.payload.b\nc = msg.payload.c\n\nvar list = [a,b,c]\nvar msg1 = {payload:list}\nreturn msg1;","outputs":1,"noerr":0,"x":970,"y":160,"wires":[["920e7a2f.0d4888"]]},{"id":"920e7a2f.0d4888","type":"debug","z":"928d9b65.5f22a","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","x":1130,"y":160,"wires":[]}]