Sample data frame is given below . It contains column names and new column that I want to create .
df1<-data.frame(city=c("Delhi","Pune","Mumbai","Bangalore","Indiranagar"),ID=c(1,1,1,2,2),expected_city_col=c("Delhi Pune Mumbai","Delhi Pune Mumbai","Delhi Pune Mumbai","Bangalore Indiranagar","Bangalore Indiranagar"))
I want to concatenate City rows by ID column , and create expected_city_col in my data frame .