aggregating data from different column [duplicate]

Question

how do I turn this dataframe

city2001 <- c('a', 'b', 'a')
grade2001 <- c(5, 5, 7)
city2002 <- c('b', 'b', 'a')
grade2002 <- c(8, 9, 10)

df <- data.frame(city2001, grade2001, city2002, grade2002)

into a data frame that looks like this:

| city | grade  |
|:---- |:------:|
| a    | 5      |
| b    | 5      |
| a    | 7      |
| b    | 8      |
| b    | 9      |
| a    | 10     |

thanks!

Answer 1

This is similar to your last question, but not exactly since you are trying to melt the data frame and keep the original values. A similar solution to the previous:

data.frame(
  "city"=unlist(df[,grepl("city",colnames(df))]),
  "grade"=unlist(df[,grepl("grade",colnames(df))])
)

          city grade
city20011    a     5
city20012    b     5
city20013    a     7
city20021    b     8
city20022    b     9
city20023    a    10