BOTTOM LINE: While I feel quite comfortable extracting elements from data.frame structures, I’m all thumbs when it comes to lists, which is kind of ironic because the data.frame structure is a kind of list…
All that said, I’m a strong believer in the power of confronting fears and addressing ones weaknesses, and today, an occasion presented itself for me to address some of my list-indexing issues. In my example I was using strsplit() to manipulate some string data. What I wanted to do was to extract the third word from a vector of strings where each element contained a name with 2+ words. After doing some hunting around I found this most helpful post that contained a solution, but also provided me with some insight on lists. Enough of that, however, here’s what I ended up doing:
V1 <- c( "Mr. Hooper's Store", "Oscar the Grouchs Can", "Big Bird's Nest" , "Maria's pad", "Elmo's Secret Hideout") V2 <- sapply(strsplit(V1, " "), function(x) x) ## the result of strsplit is a list ## this is also insightful strsplit(V1, " ")[[c(1,3)]] ## to parse things out, the magic happens with sapply V3 <- strsplit(V1, " ") V3 ## let's just change our request to the second word now, just for fun! sapply(V3, function(x) x) ## magic!
So, what I learned is that to extract specific elements from list structures, I’m going to have to lean on looping constructs and helpful R-ish loop-like functions (of the apply-ilk) to get what I want.