R-使用索引和列表内容合并两个数据框[R]

Question

Perhaps bloody obvious, but new to R. My two dataframes to be merged:

longtext <- c("bla bla burp bla blub", "blah bladd", "blablaz burp")
txt <- data.frame(longtext)
queries <- c("burp", "blah")
query <- data.frame(queries)

I performed a search for the strings in query within the longer text strings in txt . The matches were saved in a list of style:

matches <-list(c(1,3), c(2))

The first index of the list matches , eg [[1]] refers to the first row in query . The content of matches in the first row (1,3) refers to search hits row 1 and 3 in txt . So I want to merge both dataframes by using the indices and content of matches to get:

queries; longtext        
"burp"; "bla bla burp blah blub"
"burp"; "blablaz burp"
"blah"; "blah bladd"

But... my loop over indices and content doesn't work. Is there an easier way with apply() ? Will feed with lot's of data...

matches_long <- data.frame()  
for (i in 1:length(matches)) {
  for (l in 1:length(matches[[i]])) {
    matches_long[[l]] <- data.frame(query[[i]], txt[[matches[[i]][l]]])}}  

Answer 1

Seems to me like you could just add rows to your data set according to the size of matches and then just assign the matched values

res <- query[rep(seq_along(matches), sapply(matches, length)),, drop = FALSE] 
res["longtext"] <- txt$longtext[unlist(matches)]
res
#     queries              longtext
# 1      burp bla bla burp bla blub
# 1.1    burp          blablaz burp
# 2      blah            blah bladd

• in R v 3.2+ you could replace sapply(matches, length) with lengths

Answer 2

@David Arenburgs answer is better, but as I was about to paste this in:

names(matches) <- queries
stack(lapply(matches, function(x){longtext[x]}))