lapply

If I have a list of data frames list.dfs <- list(df1 = data.frame(var1 = c(1:3), var2 = c(1:3), var3 = c(1:3)), df2 = data.frame(var1= c(1:3), var2 = c(1:3), var3 = c(1:3)), df3 = data.frame(var1= c(1:3), var2 = c(1:3), var3 = c(3:1))) How do I use lapply and order to sort every data frame in the list by var3 (lowest to highest) lapply(list.dfs, function(x) x[order(x$var3), ]) will do the trick. 来源： https://stackoverflow.com/questions/21391377/order-a-data-frame-in-a-list

In R, how do you replace the following code using functions like apply , lapply , rapply , do.call , etc.? u <- 10:12 slist <- list() for (i in 1:length(u)) { p <- combn(u, i) for (j in 1:ncol(p)) { s <- paste(p[,j], collapse=",") slist[[s]] <- 0 } } For this part: for (j in 1:ncol(p)) { s <- paste(p[,j], collapse=",") I tried something like: s <- apply(p, 2, function(x) paste(x, collapse=",")) Which works. But then for that slist[[s]] <- 0 part inside that same for-loop, I don't know what to do. Edit: This is what I'm trying to do. For the vector u , I'm producing a list of all the subsets in

I have a bunch of data.tables in a list. I want to apply unique() to each data.table in my list, but doing so destroys all my data.table keys. Here's an example: A <- data.table(a = rep(c("a","b"), each = 3), b = runif(6), key = "a") B <- data.table(x = runif(6), b = runif(6), key = "x") blah <- unique(A) Here, blah still has a key, and everything is right in the world: key(blah) # [1] "a" But if I add the data.tables to a list and use lapply() , the keys get destroyed: dt.list <- list(A, B) unique.list <- lapply(dt.list, unique) # Keys destroyed here lapply(unique.list, key) # [[1]] # NULL #

I have the following list test_list=list(list(a=1,b=2),list(a=3,b=4)) and I want to extract all elements with list element name a . I can do this via sapply(test_list,`[[`,"a") which gives me the correct result #[1] 1 3 When I try the same with Rs dollar operator $ , I get NULL sapply(test_list,`$`,"a") #[[1]] #NULL # #[[2]] #NULL However, if I use it on a single element of test_list it works as expected `$`(test_list[[1]],"a") #[1] 1 Am I missing something obvious here? NGaffney From what I've been able to determine it's a combination of two things. First, the second element of $ is matched

My goal is to make another column by summing the observation from the present day and all previous observations from the same ID by using the date (the data set is sorted in date and chr nr(ID). I will need the aggregation to start over when a new "id" is presented. there might be som NA's, they should be considered as null "Doseringer_pr_kg_dyr" is the observation. CHR_NR DATO_AFSLUT Doseringer_pr_kg_dyr brugstid 10358 2018-08-06 29416.67 31 10358 2018-09-06 104682.27 36 10358 2018-10-12 10333.33 26 10358 2018-11-07 10090.91 27 10358 2018-12-04 8000.00 NA 13168 2012-01-23 12042.25 2 13168