r - Apply a function to each data frame -

i have 4 data frames contain date column, price column , return column.

data.1:

date        price  return 2009-01-02  100    0.2 2009-01-03  110    0.1 etc. 

data.2:

date        price  return 2009-02-02  60    0.15 2009-02-03  50    -0.1 etc. 

i set loop , apply function density() each data frame, returning density values returns.

i through creating list, setting loop , using lapply() this, so

> ff <- list(data.1, data.2, data.3, data.4) > for(i in 1:length(ff){         density[[i]] <- lapply(ff, density(ff[[i]]$return))} 

but doesn't work. offer me help?

thanks in advance - dani

first, should initialize density if want manual assignment.

densities <- list() 

second, use density function in funny way. should specify function different in lapply. either give function , arguments after comma, or construct own custom little function in lapply call, shown below.

data.1 <- data.frame(     x1 = letters[1:10],     x2 = 1:10 )  data.2 <- data.frame(     x1 = letters[11:20],     x2 = 10:1 )  ff <- list(data.1,data.2)  densities <- lapply(ff,function(i) {density(i$x2)}) 

this returns list automatically.

to data out of it, use list indices:

densities[[1]]$x 

if named list before, use names :

names(ff) <- c("data.1","data.2")  densities <- lapply(ff,function(i) {density(i$x2)}) densities[['data.1']]$x