How to apply a function to a list and get results as a list in R?

Question

[jzhou]

I'd like to run the below code for my table, but instead of defining "ind_gene" as a single row name and running everything based on that, I want to run mass survival analysis and extract the p-value for every gene listed in rownames(z_rna), and have R return the results to me as a list. Could anyone please point me towards a method to do this?

# pick your gene of interest
ind_gene <- which(rownames(z_rna) == "TP53")

# run survival analysis
s <- survfit(Surv(as.numeric(as.character(all_clin$new_death))[ind_clin],all_clin$death_event[ind_clin])~event_rna[ind_gene,ind_tum])
s1 <- tryCatch(survdiff(Surv(as.numeric(as.character(all_clin$new_death))[ind_clin],all_clin$death_event[ind_clin])~event_rna[ind_gene,ind_tum]), error = function(e) return(NA))

# extract the p.value
pv <- ifelseis.na(s1),next,(round(1 - pchisq(s1$chisq, length(s1$n) - 1),3)))[[1]]

Thanks so much!

[Jean-Karim Heriche]

Have a look at apply().

[Giovanni M Dall'Olio]

There is a missing parenthesis in the last row, between ifelse and is.na.

My two cents is to do this on tables instead of lists.

Answer 1

[lakhujanivijay]

You can use either apply() or lapply() functions. Here is the description:

apply()

Returns a vector or array or list of values obtained by applying a function to margins of an array or matrix.

Usage:

 apply(X, MARGIN, FUN, ...)

Arguments:

   X: an array, including a matrix.

MARGIN: a vector giving the subscripts which the function will be applied over. E.g., for a matrix ‘1’ indicates rows, ‘2’ indicates columns, ‘c(1, 2)’ indicates rows and columns. Where ‘X’ has named dimnames, it can be a character vector selecting dimension names.

 FUN: the function to be applied: see ‘Details’.  In the case of
      functions like ‘+’, ‘%*%’, etc., the function name must be
      backquoted or quoted.

 ...: optional arguments to ‘FUN’.

lapply()

 ‘lapply’ returns a list of the same length as ‘X’, each element of
 which is the result of applying ‘FUN’ to the corresponding element
 of ‘X’.

Here is a fantastic tutorial

PS: in your case lapply() is suitable because you mentioned that the output should be a list.