How to split a string into regular intervals in R?

Question

I have a long string that I want to split into regular intervals of, say, 10 words each:

x <- "Hrothgar, king of the Danes, or Scyldings, builds a great mead-hall, or palace, in which he hopes to feast his liegemen and to give them presents. The joy of king and retainers is, however, of short duration. Grendel, the monster, is seized with hateful jealousy. He cannot brook the sounds of joyance that reach him down in his fen-dwelling near the hall. Oft and anon he goes to the joyous building, bent on direful mischief. Thane after thane is ruthlessly carried off and devoured, while no one is found strong enough and bold enough to cope with the monster. For twelve years he persecutes Hrothgar and his vassals."

Using strsplit I can split the sentence into individual words:

x1 <- unlist(strsplit(x, " "))

Using paste I can paste together 10 words each:

paste(x1[1:10], collapse = " ")
paste(x1[11:20], collapse = " ")
...
paste(x1[101:110], collapse = " ")

But that's tedious, so I've tried sapply and seq:

lapply(x1, function(x) paste(x[seq(1,100,10)], collapse = " "))

but the result is not what I want. What I want is something like this:

[1] "Hrothgar, king of the Danes, or Scyldings, builds a great"
[2] "mead-hall, or palace, in which he hopes to feast his"
[3] "liegemen and to give them presents. The joy of king"
[4] "and retainers is, however, of short duration. Grendel, the monster,"
[5] "is seized with hateful jealousy. He cannot brook the sounds"
...
[10] "twelve years he persecutes Hrothgar and his vassals. NA NA"

I'm open to any solution but would be particularly grateful for a base R one.

Answer 1

Another option with only base R, using regex to capture (\\1) groups of 10 words (alphanumeric characters, which may contain hyphen, with a word bound \b), and punctuations, and put a "remarkable" string ("XXX" here) in the end, so it can be split by this string afterwards (putting a space before this string in the strsplit pattern avoids trailing space at the end of each bit):

unlist(strsplit(gsub("(((\\w|-)+\\b[ ,.]*){10})", "\\1XXX", x), " XXX"))

# [1] "Hrothgar, king of the Danes, or Scyldings, builds a great"          
# [2] "mead-hall, or palace, in which he hopes to feast his"               
# [3] "liegemen and to give them presents. The joy of king"                
# [4] "and retainers is, however, of short duration. Grendel, the monster,"
# [5] "is seized with hateful jealousy. He cannot brook the sounds"        
# [6] "of joyance that reach him down in his fen-dwelling near"            
# [7] "the hall. Oft and anon he goes to the joyous"                       
# [8] "building, bent on direful mischief. Thane after thane is ruthlessly"
# [9] "carried off and devoured, while no one is found strong"             
#[10] "enough and bold enough to cope with the monster. For"               
#[11] "twelve years he persecutes Hrothgar and his vassals."     

Answer 2

You could create a sequence and paste the words from x1 :

sapply(seq(1, length(x1), 10), function(i) 
       paste0(x1[i:min(i + 9, length(x1))], collapse = " "))

# [1] "Hrothgar, king of the Danes, or Scyldings, builds a great"          
# [2] "mead-hall, or palace, in which he hopes to feast his"               
# [3] "liegemen and to give them presents. The joy of king"                
# [4] "and retainers is, however, of short duration. Grendel, the monster,"
# [5] "is seized with hateful jealousy. He cannot brook the sounds"        
# [6] "of joyance that reach him down in his fen-dwelling near"            
# [7] "the hall. Oft and anon he goes to the joyous"                       
# [8] "building, bent on direful mischief. Thane after thane is ruthlessly"
# [9] "carried off and devoured, while no one is found strong"             
#[10] "enough and bold enough to cope with the monster. For"               
#[11] "twelve years he persecutes Hrothgar and his vassals."        

Answer 3

You can use gregexpr with regmatches and quantify the words with {1,10}.

trimws(regmatches(x, gregexpr("([^[:space:]]+\\s*){1,10}", x))[[1]])
# [1] "Hrothgar, king of the Danes, or Scyldings, builds a great"          
# [2] "mead-hall, or palace, in which he hopes to feast his"               
# [3] "liegemen and to give them presents. The joy of king"                
# [4] "and retainers is, however, of short duration. Grendel, the monster,"
# [5] "is seized with hateful jealousy. He cannot brook the sounds"        
# [6] "of joyance that reach him down in his fen-dwelling near"            
# [7] "the hall. Oft and anon he goes to the joyous"                       
# [8] "building, bent on direful mischief. Thane after thane is ruthlessly"
# [9] "carried off and devoured, while no one is found strong"             
#[10] "enough and bold enough to cope with the monster. For"               
#[11] "twelve years he persecutes Hrothgar and his vassals."               

Answer 4

Hope this might help

sapply(
  unname(split(
    y <- unlist(strsplit(x, " ")),
    ceiling(seq_along(y) / 10)
  )),
  paste,
  collapse = " "
)

which gives

 [1] "Hrothgar, king of the Danes, or Scyldings, builds a great"
 [2] "mead-hall, or palace, in which he hopes to feast his"
 [3] "liegemen and to give them presents. The joy of king"
 [4] "and retainers is, however, of short duration. Grendel, the monster,"
 [5] "is seized with hateful jealousy. He cannot brook the sounds"
 [6] "of joyance that reach him down in his fen-dwelling near"
 [7] "the hall. Oft and anon he goes to the joyous"
 [8] "building, bent on direful mischief. Thane after thane is ruthlessly"
 [9] "carried off and devoured, while no one is found strong"
[10] "enough and bold enough to cope with the monster. For"
[11] "twelve years he persecutes Hrothgar and his vassals."

Answer 5

using stringr:

library(stringr)
N = length(strsplit(x, ' ')[[1]]) 
start = seq.int(1, N, 10)
end = start+9
end[length(end)] = N
word(x, start, end)

# [1] "Hrothgar, king of the Danes, or Scyldings, builds a great"          
# [2] "mead-hall, or palace, in which he hopes to feast his"               
# [3] "liegemen and to give them presents. The joy of king"                
# [4] "and retainers is, however, of short duration. Grendel, the monster,"
# [5] "is seized with hateful jealousy. He cannot brook the sounds"        
# [6] "of joyance that reach him down in his fen-dwelling near"            
# [7] "the hall. Oft and anon he goes to the joyous"                       
# [8] "building, bent on direful mischief. Thane after thane is ruthlessly"
# [9] "carried off and devoured, while no one is found strong"             
# [10] "enough and bold enough to cope with the monster. For"               
# [11] "twelve years he persecutes Hrothgar and his vassals."