[R] Odp: Extracting values in table

[Petr PIKAL]

Hi

> Hi All,
> 
> I am a beginner in programming in r and please do forgive me if my 
question
> seems to be silly and sometimes not understandable. 
> 
> 1. we have a list of elements in a list say:
> 
> ls<-list("N","E","E","N","P","E","M","Q","E","M")
> 
> 2. We have an another list of tables in a list say:
> 
> n <- list("M", "N","E","P","Q","M","N","E","Q","N")
> 
> tb <- lapply(1:10, function(i)matrix(sample(4), 2, 2,
> dimnames=list(n[sample(10,2)], n[sample(2,2)])))
> 
> 3. we need to extract values from the table in the list where colname is
> always "M" , wherein the rowname should be the 1st element in the list 
ls
> for table 1 in the list tb and 2nd element in table 2 and so on...
> 
> for ex: 
>    M N
> N 4 1
> P 3 2
> 
> In table 1 , we need to extract value 4.

I can not provide you with canned solution but

x = sapply(tb, function(x) which(dimnames(x)[[2]]=="M"))

gives you vector of M positions in column names

for (i in seq_along(ls1)) print(which(rownames(tb[[i]]) %in% ls[[i]]))

# for (i in seq_along(ls1)) y[i] <- which(rownames(tb[[i]]) %in% ls[[i]])
# does not work as there is sometimes no match

gives you position of row names (if they exist)

then you can use that for selection of items from list tb

e.g. for the first table

tb[[1]][x[1],y[[1]]]

> tb[[1]]
  M N
N 3 2
Q 1 4

tb[[1]][x[1],y[1]]
[1] 3

Regards
Petr

> 
> 
> Thanks to all in advance.
> 
> 
> 
> 
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