[R] Create blocks or observations

[Sharpie]

tj wrote:
> 
> Anyone who can help me with this?
> I have 48 observations (I dont want to alter their order). I want to group
> these observations into 16 blocks. So I should have 3 observations for
> each block. This is what I did in R, but it has warnings. 
> 
>> y                 #contains my 48 observations
>  [1] 2.4 2.4 2.4 2.2 2.1 1.5 2.3 2.3 2.5 2.0 1.9 1.7 2.2 1.8 3.2 3.2 2.7
> 2.2 2.2
> [20] 1.9 1.9 1.8 2.7 3.0 2.3 2.0 2.0 2.9 2.9 2.7 2.7 2.3 2.6 2.4 1.8 1.7
> 1.5 1.4
> [39] 2.1 3.3 3.5 3.5 3.1 2.6 2.1 3.4 3.0 2.9
>> g=c(0,0,0)         #storage vector
>> for (i in 1:16){  
> + g[i]=y[(3*i-2) : (3*i)]
> + }
> There were 16 warnings (use warnings() to see them)
>> g[1]
> [1] 2.4
>> g[2]
> [1] 2.2
>> 
> 
> ###### g[1] should show 2.4 2.4 2.4
> ###### g[2] should show 2.2 2.1 1.5
> ######g[16] should show 3.4 3.0 2.9
> 
> Can you please tell me how I should correct my program?
> Thank you.
> 
> ~tj
> 

I think your main problem is that you created a vector g[] which is three
elements long.  Then you tried to set a single element of g equal to three
elements of y which doesn't work too well- you can't wedge a vector of
length 3 into a box designed to hold one element.

I would suggest paring y with a "group" vector that indicates which group
each element of y belongs to:

  numGroups <- length( y ) / 3

  group <- unlist( lapply( 1:numGroups, rep.int, times = 3 ) )

Then you can use the split function to break y apart based on group:

  split( y, group )

Or you could pair them as columns in a data frame and use split() to split
into sub-data frames or by() to split and execute a function on each
sub-data frame.

Hope this helps!

-Charlie

-----
Charlie Sharpsteen
Undergraduate-- Environmental Resources Engineering
Humboldt State University
-- 
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