[R] Using split() several times in a row?

[Sergey Goriatchev]

Hi, fellow R users.

I have a question about sapply and split combination.

I have a big dataframe (40000 observations, 21 variables). First
variable (factor) is "date" and it is in format "8.29.97", that is, I
have monthly data. Second variable (also factor) has levels 1 to 6
(fractiles 1 to 5 and missing value with code 6). The other 19
variables are numeric.
For each month I have several hunder observations of 19 numeric and 1 factor.

I am normalizing the numeric variables by dividing val1 by val2, where:

val1: (for each month, for each numeric variable) difference between
mean of ith numeric variable in fractile 1, and mean of ith numeric
variable in fractile 5.

val2: (for each month, for each numeric variable) standard deviation
for ith numeric variable.

Basically, as far as I understand, I need to use split() function several times.
To calculate val1 I need to use split() twice - first to split by
month and then split by fractile. Is this even possible to do (since
after first application of split() I get a list)??

Is there a smart way to perform this normalization computation?

My knowledge of R is not so advanced, but I need to know an efficient
way to perform calculations of this kind.

Would really appreciate some help from experienced R users!

Regards,
S

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