[R] how to sort new data frame based on the original data frame

[Joshua Wiley]

Hi,

On Tue, Jan 11, 2011 at 9:19 AM, wangwallace <talenttree at gmail.com> wrote:
>
> I have a really simple question
>
> I have a data frame of 8 variables (the first column is the subjects' id):
>
>    SubID     G1    G2     G3     G4    W1    W2      W3    W4
>      1          6      5       6       2      6      2        2       4
>      2          6      4       7       2      6      6        2       3
>      3          5      5       5       5      5      5        4       5
>      4          5      4       3       4      4      4        5       2
>      5          5      6       7       5      6      4        4       1
>      6          5      4       3       6      4      3        7       3
>      7          3      6       6       3      6      5        2       1
>      8          3      6       6       3      6      5        4       7
>
>
> this data frame have two sets of variables. each set simply represent one
> scale. as shown above, the first scale, say G, consists of four items: G1,
> G2, G3, and G4, whereas the second scale, say W, also has four items: W1,
> W2, W3, W4.
> the leftmost column lists the subjects' ID.
>
> I drew 100 new random samples based on the data frame. here is the structure
> of each new random sample:
>               var    var   var     var
>                g      g      g       g
>                g      g      g       g
>                w      w     w       w
>                w      w     w       w
>                w      w     w       w
>                w      w     w       w
>                w      w     w       w
>                w      w     w       w
>
> each random sample satisfies the following rules:
>
> ###the top two rows have to be filled with 2 random rows of the 8 rows of G
> numbers. the rest should be filled with 6 random rows of the 8 rows of W
> numbers. At the same time, the SubIDs of all eight rows should be different
> among each other.
>
> here below is the syntax I've used:
>
>> fff<-function(dat,g=2,w=6){
> + sel1<-sample(1:8,g)
> + sel2<-sample((1:8)[-sel1],w)
> + M=dat[sel1,2:5]
> + N=dat[sel2,6:9]
> + colnames(N)<-colnames(M)
## just add the order to rbind()
> + rbind(M, N)[order(c(sel1, sel2)), ]
> +}

>> result<-vector("list",100)
>> for(i in 1:100)result[[i]]<-fff(data,2,6)
>> result

For convenience and speed, consider building this (the for loop) into
your function.  The only part that you actually need looped is the
sample(), so you could get some performance gains, if you are
interested/that is an issue.

HTH,

Josh

-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/