R shiny aggregate function

[goood0001]

dta_agg<-aggregate(dta[,"id"]~passenger_count,dta,mean)
barplot(dta_agg[,2],names.arg = dta$passenger_count,main=input$passenger_count,
ylab="Number of Pickup location",xlab="users")
This is the code i have tried and got an error :"incorrect number of names". Can you help me with this aggregate function.