[R] loop on list levels and names

[Matthew Dowle]

One way is :

dataset = data.table(ssfamed)
dataset[, < whatever "some functions" are on Asfc, Smc, epLsar, etc >, 
by="SPECSHOR,BONE"]

Your SPECSHOR and BONE names will be in your result alongside the results of 
the <whatever ...>

Or try package plyr which does this sort of thing too.  And sqldf may be 
better if you know SQL and prefer it.  There are actually zillions of ways 
to do it : by(), doBy() etc etc

If you get your code working the way its constructed currently,  its going 
to be very slow, because of those "==".   data.table doesn't do that and is 
pretty fast for this kind of thing. You might find that plyr is easier to 
use and more flexible though if speed isn't an issue,  depending on exactly 
what you want to do.

Whichever way you decide,  consider voting on crantastic for the package you 
end up using,  and that may be a quick and easy way for you to help new R 
users in the future, and help us all by reducing the r-help traffic on the 
same subject over and over again.

Note that plyr is the 2nd spot on crantastic,  it would have solved your 
problem without needing to write that code.  If you check crantastic first 
and make sure you're aware of popular packages, it might avoid getting stuck 
in this way again.  It only works if users contribute to it though.


"Ivan Calandra" <ivan.calandra at uni-hamburg.de> wrote in message 
news:4B587CDD.4070209 at uni-hamburg.de...
> Hi everybody!
>
> To use some functions, I have to transform my dataset into a list, where
> each element contains one group, and I have to prepare a list for each
> variable I have (altogether I have 15 variables, and many entries per
> factor level)
>
> Here is some part of my dataset:
> SPECSHOR    BONE    Asfc    Smc    epLsar
> cotau    tx    454.390369    29.261638    0.001136
> cotau    tx    117.445711    4.291884    0.00056
> cotau    tx    381.024682    15.313017    0.002324
> cotau    tx    159.081789    18.134533    0.000462
> cotau    tm    160.641503    6.411332    0.000571
> cotau    tm    79.238023    3.828254    0.001182
> cotau    tm    143.20655    11.921899    0.000192
> cotau    tm    115.476996    33.116386    0.000417
> cotau    tm    594.256234    72.538131    0.000477
> eqgre    tx    188.261324    8.279096    0.000777
> eqgre    tx    152.444216    2.596325    0.001022
> eqgre    tx    256.601507    8.279096    0.000566
> eqgre    tx    250.816445    18.134533    0.000535
> eqgre    tx    272.396711    24.492879    0.000585
> eqgre    tm    172.63264    4.291884    0.001781
> eqgre    tm    189.441097    14.425498    0.001347
> eqgre    tm    170.743788    13.564472    0.000602
> eqgre    tm    158.960849    10.385299    0.001189
> eqgre    tm    80.972408    3.828254    0.000644
> gicam    tx    294.494001    9.656738    0.000524
> gicam    tx    267.126765    19.128024    0.000647
> gicam    tx    81.888658    4.782006    0.000492
> gicam    tx    168.32908    12.729939    0.001097
> gicam    tx    123.296056    7.007427    0.000659
> gicam    tm    94.264887    18.134533    0.000752
> gicam    tm    54.317395    3.828254    0.00038
> gicam    tm    55.978883    17.167534    0.000141
> gicam    tm    279.597993    15.313017    0.000398
> gicam    tm    288.262556    18.134533    0.001043
>
> What I do next is:
> ----
> list_Asfc <- list()
> list_Asfc[[1]] <- ssfamed[ssfamed$SPECSHOR=='cotau'&ssfamed$BONE=='tx', 3]
> list_Asfc[[2]] <- ssfamed[ssfamed$SPECSHOR=='cotau'&ssfamed$BONE=='tm', 3]
> ----
>
> And so on for each level of SPECSHOR and BONE
>
> I'm stuck on 2 parts:
> - in a loop or something similar, I would like the 1st element of the
> list to be filled by the values for the 1st variable with the first
> level of my factors (i.e. cotau + tx), and then the 2nd element with the
> 2nd level (i.e. cotau + tm) and so on. As shown above, I know how to do
> it if I enter manually the different levels, but I have no idea which
> function I should use so that each combination of factor will be used.
> See what I mean?
>
> - I would then like to run it in a loop or something for each variable.
> It is by itself not so complicated, but I don't know how to give the
> correct name to my list. I want the list containing the data for Asfc to
> be named "list_Asfc".
> Here is what I tried:
> ----
> seq.num <- c(seq(3,5,1))     #the indexes of the variables
> for(i in 1:length(seq.num)) {
>  k <- seq.num[i]
>  name.num <- names(ssfamed)[k]
>  list <- list()
>  list[[1]] <- ssfamed[ssfamed$SPECSHOR=='cotau'&ssfamed$BONE=='tx', i]
>  list[[2]] <- ssfamed[ssfamed$SPECSHOR=='cotau'&ssfamed$BONE=='tm', i]
>  names(list) <- c("cotau_tx", "cotau_tm")     #I have more and the 1st
> question should help me on that too
> }
> ----
> After names(list) I need to insert something like: name_list <- list
> But I don't know how to give it the correct name. How do we change the
> name of an object? Or am I on the wrong path?
>
> Thank you in advance for your help.
> Ivan
>
> PS: if necessary: under Windows XP, R2.10.
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