[R] Complex sampling?

[Hosack, Michael]

R users,

I am trying to generate a randomized weekday survey schedule that ensures even coverage of weekdays in 
the sample, where the distribution of variable DOW is random with respect to WEEK. To accomplish this I need 
to randomly sample without replacement two weekdays per week for each of 27 weeks (only 5 are shown). However, 
I need to sample from a sequence (3:7) that needs to be completely depleted and replenished until the 
final selection is made. Here is an example of what I want to do, beginning at WEEK 1. I would prefer to do 
this without using a loop, if possible. 

sample frame: [3,4,5,6,7] --> [4,5,6] --> [4],[1,2,3,(4),5,6] --> [1,2,4,5,6] --> for each WEEK in dataframe

Randomly sample 2 DOW_NUM without replacement from each WEEK ( () = no two identical DOW_NUM can be sampled 
in the same WEEK)
      
sample = {3,7}, {5,6}, {4,3}, {1,5}, --> for each WEEK in dataframe


Thanks you,

Mike


         DATE DOW DOW_NUM WEEK
2  2011-05-02 Mon       3    1
3  2011-05-03 Tue       4    1
4  2011-05-04 Wed       5    1
5  2011-05-05 Thu       6    1
6  2011-05-06 Fri       7    1
9  2011-05-09 Mon       3    2
10 2011-05-10 Tue       4    2
11 2011-05-11 Wed       5    2
12 2011-05-12 Thu       6    2
13 2011-05-13 Fri       7    2
16 2011-05-16 Mon       3    3
17 2011-05-17 Tue       4    3
18 2011-05-18 Wed       5    3
19 2011-05-19 Thu       6    3
20 2011-05-20 Fri       7    3
23 2011-05-23 Mon       3    4
24 2011-05-24 Tue       4    4
25 2011-05-25 Wed       5    4
26 2011-05-26 Thu       6    4
27 2011-05-27 Fri       7    4
30 2011-05-30 Mon       3    5
31 2011-05-31 Tue       4    5
32 2011-06-01 Wed       5    5
33 2011-06-02 Thu       6    5
34 2011-06-03 Fri       7    5

DF <-
structure(list(DATE = structure(c(15096, 15097, 15098, 15099, 
15100, 15103, 15104, 15105, 15106, 15107, 15110, 15111, 15112, 
15113, 15114, 15117, 15118, 15119, 15120, 15121, 15124, 15125, 
15126, 15127, 15128), class = "Date"), DOW = c("Mon", "Tue", 
"Wed", "Thu", "Fri", "Mon", "Tue", "Wed", "Thu", "Fri", "Mon", 
"Tue", "Wed", "Thu", "Fri", "Mon", "Tue", "Wed", "Thu", "Fri", 
"Mon", "Tue", "Wed", "Thu", "Fri"), DOW_NUM = c(3, 4, 5, 6, 7, 
3, 4, 5, 6, 7, 3, 4, 5, 6, 7, 3, 4, 5, 6, 7, 3, 4, 5, 6, 7), 
    WEEK = c(1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 
    4, 4, 4, 4, 5, 5, 5, 5, 5)), .Names = c("DATE", "DOW", "DOW_NUM", 
"WEEK"), row.names = c(2L, 3L, 4L, 5L, 6L, 9L, 10L, 11L, 12L, 
13L, 16L, 17L, 18L, 19L, 20L, 23L, 24L, 25L, 26L, 27L, 30L, 31L, 
32L, 33L, 34L), class = "data.frame")