[R] loop on list levels and names

[Don MacQueen]

Without reading all the details of your question, it looks like maybe 
split() is what you want.

  split( dataset, paste(dataset$SPECSHOR,dataset$BONE) )

or

   split( dataset[,3], paste(dataset$SPECSHOR,dataset$BONE) )

-Don

At 5:12 PM +0100 1/21/10, Ivan Calandra wrote:
>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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-- 
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062