[R] Randomly sampling subsets of dataframe variable

[Ali Tofigh]

I would just get row indices:

row.indices <- as.vector(sapply(0:25 * 5 + 1, function(x)
{sort(sample(x:(x+4), 2))}))
new.data.fram <- your.data.frame[row.indices, ]

Cheers,
/Ali

On Fri, Mar 12, 2010 at 15:06, Hosack, Michael <mhosack at state.pa.us> wrote:
> Fellow R users,
>
> I am stumped on what would seem to be something fairly simple.
> I have a dataframe that has a variable named 'WEEK' that takes
> the numbers 1:26 (26 week time-period) with each number repeated
> five times consecutively (once for each weekday, Monday through
> Friday). Ex. 111112222233333.....2626262626. I would like to
> randomly extract two weekdays per five day week for each of
> 26 weeks and store this data as a separate dataframe. I have
> been unable to get the sample function to work properly.
> I have also tried using the runif function to assign random
> numbers to each row of my dataframe, sort the dataframe first
> by week number then by random number value, and finally select
> the first two elements from each week subset (26 weeks total,
> giving 52 randomly selected values).  I can't figure out how
> to select the first two elements. My goal is to randomly
> select two weekdays per week (without replacement) for each of
> 26 consecutive weeks. Any advice would be greatly appreciated.
>
> Thank you,
>
> Mike
>
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