问题
Is there a function to count the number of words in a string? For example:
str1 <- \"How many words are in this sentence\"
to return a result of 7.
回答1:
You can use strsplit and sapply functions
sapply(strsplit(str1, " "), length)
回答2:
Use the regular expression symbol \\W to match non-word characters, using + to indicate one or more in a row, along with gregexpr to find all matches in a string. Words are the number of word separators plus 1.
lengths(gregexpr("\\W+", str1)) + 1
This will fail with blank strings at the beginning or end of the character vector, when a "word" doesn't satisfy \\W's notion of non-word (one could work with other regular expressions, \\S+, [[:alpha:]], etc., but there will always be edge cases with a regex approach), etc. It is likely more efficient than strsplit solutions, which will allocate memory for each word. Regular expressions are described in ?regex.
Update As noted in the comments and in a different answer by @Andri the approach fails with (zero) and one-word strings, and with trailing punctuation
str1 = c("", "x", "x y", "x y!" , "x y! z")
lengths(gregexpr("[A-z]\\W+", str1)) + 1L
# [1] 2 2 2 3 3
Many of the other answers also fail in these or similar (e.g., multiple spaces) cases. I think my answer's caveat about 'notion of one word' in the original answer covers problems with punctuation (solution: choose a different regular expression, e.g., [[:space:]]+), but the zero and one word cases are a problem; @Andri's solution fails to distinguish between zero and one words. So taking a 'positive' approach to finding words one might
sapply(gregexpr("[[:alpha:]]+", str1), function(x) sum(x > 0))
Leading to
sapply(gregexpr("[[:alpha:]]+", str1), function(x) sum(x > 0))
# [1] 0 1 2 2 3
Again the regular expression might be refined for different notions of 'word'.
I like the use of gregexpr() because it's memory efficient. An alternative using strsplit() (like @user813966, but with a regular expression to delimit words) and making use of the original notion of delimiting words is
lengths(strsplit(str1, "\\W+"))
# [1] 0 1 2 2 3
This needs to allocate new memory for each word that is created, and for the intermediate list-of-words. This could be relatively expensive when the data is 'big', but probably it's effective and understandable for most purposes.
回答3:
Most simple way would be:
require(stringr)
str_count("one, two three 4,,,, 5 6", "\\S+")
... counting all sequences on non-space characters (\\S+).
But what about a little function that lets us also decide which kind of words we would like to count and which works on whole vectors as well?
require(stringr)
nwords <- function(string, pseudo=F){
ifelse( pseudo,
pattern <- "\\S+",
pattern <- "[[:alpha:]]+"
)
str_count(string, pattern)
}
nwords("one, two three 4,,,, 5 6")
# 3
nwords("one, two three 4,,,, 5 6", pseudo=T)
# 6
回答4:
I use the str_count function from the stringr library with the escape sequence \w that represents:
any ‘word’ character (letter, digit or underscore in the current locale: in UTF-8 mode only ASCII letters and digits are considered)
Example:
> str_count("How many words are in this sentence", '\\w+')
[1] 7
Of all other 9 answers that I was able to test, only two (by Vincent Zoonekynd, and by petermeissner) worked for all inputs presented here so far, but they also require stringr.
But only this solution works with all inputs presented so far, plus inputs such as "foo+bar+baz~spam+eggs" or "Combien de mots sont dans cette phrase ?".
Benchmark:
library(stringr)
questions <-
c(
"", "x", "x y", "x y!", "x y! z",
"foo+bar+baz~spam+eggs",
"one, two three 4,,,, 5 6",
"How many words are in this sentence",
"How many words are in this sentence",
"Combien de mots sont dans cette phrase ?",
"
Day after day, day after day,
We stuck, nor breath nor motion;
"
)
answers <- c(0, 1, 2, 2, 3, 5, 6, 7, 7, 7, 12)
score <- function(f) sum(unlist(lapply(questions, f)) == answers)
funs <-
c(
function(s) sapply(gregexpr("\\W+", s), length) + 1,
function(s) sapply(gregexpr("[[:alpha:]]+", s), function(x) sum(x > 0)),
function(s) vapply(strsplit(s, "\\W+"), length, integer(1)),
function(s) length(strsplit(gsub(' {2,}', ' ', s), ' ')[[1]]),
function(s) length(str_match_all(s, "\\S+")[[1]]),
function(s) str_count(s, "\\S+"),
function(s) sapply(gregexpr("\\W+", s), function(x) sum(x > 0)) + 1,
function(s) length(unlist(strsplit(s," "))),
function(s) sapply(strsplit(s, " "), length),
function(s) str_count(s, '\\w+')
)
unlist(lapply(funs, score))
Output:
6 10 10 8 9 9 7 6 6 11
回答5:
str2 <- gsub(' {2,}',' ',str1)
length(strsplit(str2,' ')[[1]])
The gsub(' {2,}',' ',str1) makes sure all words are separated by one space only, by replacing all occurences of two or more spaces with one space.
The strsplit(str,' ') splits the sentence at every space and returns the result in a list. The [[1]] grabs the vector of words out of that list. The length counts up how many words.
> str1 <- "How many words are in this sentence"
> str2 <- gsub(' {2,}',' ',str1)
> str2
[1] "How many words are in this sentence"
> strsplit(str2,' ')
[[1]]
[1] "How" "many" "words" "are" "in" "this" "sentence"
> strsplit(str2,' ')[[1]]
[1] "How" "many" "words" "are" "in" "this" "sentence"
> length(strsplit(str2,' ')[[1]])
[1] 7
回答6:
You can use str_match_all, with a regular expression that would identify your words.
The following works with initial, final and duplicated spaces.
library(stringr)
s <- "
Day after day, day after day,
We stuck, nor breath nor motion;
"
m <- str_match_all( s, "\\S+" ) # Sequences of non-spaces
length(m[[1]])
回答7:
Try this function from stringi package
require(stringi)
> s <- c("Lorem ipsum dolor sit amet, consectetur adipisicing elit.",
+ "nibh augue, suscipit a, scelerisque sed, lacinia in, mi.",
+ "Cras vel lorem. Etiam pellentesque aliquet tellus.",
+ "")
> stri_stats_latex(s)
CharsWord CharsCmdEnvir CharsWhite Words Cmds Envirs
133 0 30 24 0 0
回答8:
You can use wc function in library qdap:
> str1 <- "How many words are in this sentence"
> wc(str1)
[1] 7
回答9:
You can remove double spaces and count the number of " " in the string to get the count of words. Use stringr and rm_white {qdapRegex}
str_count(rm_white(s), " ") +1
回答10:
Try this
length(unlist(strsplit(str1," ")))
回答11:
The solution 7 does not give the correct result in the case there's just one word. You should not just count the elements in gregexpr's result (which is -1 if there where not matches) but count the elements > 0.
Ergo:
sapply(gregexpr("\\W+", str1), function(x) sum(x>0) ) + 1
回答12:
Use nchar
if vector of strings is called x
(nchar(x) - nchar(gsub(' ','',x))) + 1
Find out number of spaces then add one
回答13:
Also from stringi package, the straight forward function stri_count_words
stringi::stri_count_words(str1)
#[1] 7
回答14:
require(stringr)
str_count(x,"\\w+")
will be fine with double/triple spaces between words
All other answers have issues with more than one space between the words.
回答15:
require(stringr)
Define a very simple function
str_words <- function(sentence) {
str_count(sentence, " ") + 1
}
Check
str_words(This is a sentence with six words)
回答16:
With stringr package, one can also write a simple script that could traverse a vector of strings for example through a for loop.
Let's say
df$text
contains a vector of strings that we are interested in analysing. First, we add additional columns to the existing dataframe df as below:
df$strings = as.integer(NA)
df$characters = as.integer(NA)
Then we run a for-loop over the vector of strings as below:
for (i in 1:nrow(df))
{
df$strings[i] = str_count(df$text[i], '\\S+') # counts the strings
df$characters[i] = str_count(df$text[i]) # counts the characters & spaces
}
The resulting columns: strings and character will contain the counts of words and characters and this will be achieved in one-go for a vector of strings.
回答17:
I've found the following function and regex useful for word counts, especially in dealing with single vs. double hyphens, where the former generally should not count as a word break, eg, well-known, hi-fi; whereas double hyphen is a punctuation delimiter that is not bounded by white-space--such as for parenthetical remarks.
txt <- "Don't you think e-mail is one word--and not two!" #10 words
words <- function(txt) {
length(attributes(gregexpr("(\\w|\\w\\-\\w|\\w\\'\\w)+",txt)[[1]])$match.length)
}
words(txt) #10 words
Stringi is a useful package. But it over-counts words in this example due to hyphen.
stringi::stri_count_words(txt) #11 words
来源：https://stackoverflow.com/questions/8920145/count-the-number-of-all-words-in-a-string