Store variables in a list when looping

The following list "ls" contains three data frames:

unigrams = data.frame(freq = c(3, 3, 5, 4, 3, 41), term = c("a-list", "a-p", "aaa", "aam", "aamir", "aaron")) bigrams = data.frame(freq = c(13, 1, 1, 2, 1, 4), term = c("a a", "a abode", "a about", "a absolutely", "a accessory", "a acre")) trigrams = data.frame(freq = c(1, 1, 1, 1, 1, 1), term = c("a a card", "a a divorce", "a a dreamer", "a a great", "a a guy", "a a hand")) ls = list(unigrams, bigrams, trigrams) 

Which give us this:

[[1]] freq term 1 3 a-list 2 3 a-p 3 5 aaa 4 4 aam 5 3 aamir 6 41 aaron [[2]] freq term 1 13 a a 2 1 a abode 3 1 a about 4 2 a absolutely 5 1 a accessory 6 4 a acre [[3]] freq term 1 1 a a card 2 1 a a divorce 3 1 a a dreamer 4 1 a a great 5 1 a a guy 6 1 a a hand 

I want to separate the column "term" in each data frame by the number of words, creating the columns "word1", "word2", "word3". Like this:

 freq word1 1 3 a-list 2 3 a-p 3 5 aaa 4 4 aam 5 3 aamir 6 41 aaron freq word1 word2 1 13 a a 2 1 a abode 3 1 a about 4 2 a absolutely 5 1 a accessory 6 4 a acre freq word1 word2 word3 1 1 a a card 2 1 a a divorce 3 1 a a dreamer 4 1 a a great 5 1 a a guy 6 1 a a hand 

My try:

new_ls = list() for (i in length(ls)) { x = ls[[i]] # Split each word in column "term": x[,paste("word", 1:i, sep = "")] = as.character(lapply(strsplit(as.character(x$term), split=" "), "[", i)) x = subset(x, select = -term) new_ls[[i]] = x } 

Unfortunately, this last snippet only stores some wrong result in the last element:

[[1]] NULL [[2]] NULL [[3]] freq word1 word2 word3 1 1 card card card 2 1 divorce divorce divorce 3 1 dreamer dreamer dreamer 4 1 great great great 5 1 guy guy guy 6 1 hand hand hand 

What am I doing wrong?