我想输入一个可以在此之前声明的输入：
GroupVar2 = recommendation$Product
prof.prod <- recommendation %>% group_by(GroupVar2) %>% summarise(value =
sum(Revenue)) %>% filter(value==max(value))
但是，我收到“列GroupVar2未知”的错误。
有人知道如何使用占位符中指定的“ recommendation $ Product”吗？
答案 0 :(得分：2)
由于 Error: connect ETIMEDOUT
[0] at Connection._handleConnectTimeout (C:\Watson\data-cap\node_modules\mysql\lib\Connection.js:411:13)
[0] at Object.onceWrapper (events.js:313:30)
[0] at emitNone (events.js:106:13)
[0] at Socket.emit (events.js:208:7)
[0] at Socket._onTimeout (net.js:407:8)
[0] at ontimeout (timers.js:475:11)
[0] at tryOnTimeout (timers.js:310:5)
[0] at Timer.listOnTimeout (timers.js:270:5)
[0] --------------------
[0] at Protocol._enqueue (C:\Watson\data-cap\node_modules\mysql\lib\protocol\Protocol.js:144:48)
[0] at Protocol.handshake (C:\Watson\data-cap\node_modules\mysql\lib\protocol\Protocol.js:51:23)
[0] at Connection.connect (C:\Watson\data-cap\node_modules\mysql\lib\Connection.js:118:18)
[0] at Connection._implyConnect (C:\Watson\data-cap\node_modules\mysql\lib\Connection.js:453:10)
[0] at Connection.query (C:\Watson\data-cap\node_modules\mysql\lib\Connection.js:198:8)
[0] at Object.<anonymous> (C:\Watson\data-cap\db.js:26:12)
[0] at Module._compile (module.js:643:30)
[0] at Object.Module._extensions..js (module.js:654:10)
[0] at Module.load (module.js:556:32)
[0] at tryModuleLoad (module.js:499:12)
在数据帧group_by中寻找列GroupVar2而产生错误。
如果需要使用占位符recommendation，则可以使用 GroupVar2 来取消引用 !!中的参数：< / p>
group_by通过这种方式评估输入。