summary_mean<-data%>%
+     mutate(tercile = ntile(slope3, 5))%>%      # arrange the data into 5 groups by slope3
+     group_by(tercile)%>%
+     summarise(
+       SIZE= mean(data$SIZE, na.rm=T),
+       B.M= mean(data$B.M, na.rm=T),
+       MOM= mean(data$MOM, na.rm=T),
+       LEV= mean(data$LEV, na.rm=T),
+       TO= mean(data$TO, na.rm=T))
>   summary_mean<-as.matrix(summary_mean)
>   #tbl_df(summary_mean)
> portfolio1[1,2]=summary_mean[1,"SIZE"]
Error in portfolio1[1, 2] = summary_mean[1, "SIZE"] :
  incorrect number of subscripts on matrix