Trying to sort two columns of an array in R

Question

Assume my data (df) looks something like this:

Rank    Student    Points    Type
3       Liz        60        Junior
1       Sarah      100       Junior
10      John       40        Senior
2       Robert     70        Freshman
13      Jackie     33        Freshman
11      Stevie     35        Senior

I want to sort the data according to the Points, followed by Rank column in descending and ascending order, respectively, so that it looks like this:

Rank    Student    Points    Type
1       Sarah      100       Junior
2       Robert     70        Freshman
3       Liz        60        Junior
10      John       40        Senior
11      Stevie     35        Senior
13      Jackie     33        Freshman

So I did this:

df[order(df[, "Points"], df[, "Rank"]), ]

Resulted in this:

Rank    Student    Points    Type
1       Sarah      100       Junior
10      John       40        Senior
11      Stevie     35        Senior
13      Jackie     33        Freshman
2       Robert     70        Freshman
3       Liz        60        Junior

Question: How do I fix this?

I'm trying to use the column headers because the column length/width may change which can affect my sorting if I use physical locations.

FYI: I've tried so many suggestions and none seems to work: one, two, three and four...

Answer 1

Try this:

df[order(df$Points,decreasing=T,df$Rank),]



 Rank Student Points     Type
2    1   Sarah    100   Junior
4    2  Robert     70 Freshman
1    3     Liz     60   Junior
3   10    John     40   Senior
6   11  Stevie     35   Senior
5   13  Jackie     33 Freshman

Answer 2

going back to the basics :) http://www.statmethods.net/management/sorting.html

so, your code should be: df <- df[order(-Points, Rank),]

Answer 3

Like m0nhawk pointed out in his comment, you probably have the data as strings. String characters are ordered one at a time.

You need to convert them to numeric first. Also, for decreasing order you need the argument decreasing = TRUE.

df[, "Rank"] <- as.numeric(df[, "Rank"])
df[, "Points"] <- as.numeric(df[, "Points"])
df[order(df[, "Points"], decreasing = TRUE, df[, "Rank"]), ]

If the data type is 'factor' this will not work, though. You can try the following:

df <- as.data.frame(df, stringsAsFactors = FALSE)

And then the three lines above will work.