How can two strings be concatenated?

问题:

How can I concatenate (merge, combine) two values? For example I have:

tmp = cbind(\"GAD\", \"AB\")
tmp
#      [,1]  [,2]
# [1,] \"GAD\" \"AB\"

My goal is to concatenate the two values in \"tmp\" to one string:

tmp_new = \"GAD,AB\"

Which function can do this for me?

回答1:

paste()

is the way to go. As the previous posters pointed out, paste can do two things:

concatenate values into one \"string\", e.g.

> paste(\"Hello\", \"world\", sep=\" \")
[1] \"Hello world\"

where the argument sep specifies the character(s) to be used between the arguments to concatenate, or collapse character vectors

> x <- c(\"Hello\", \"World\")
> x
[1] \"Hello\" \"World\"
> paste(x, collapse=\"--\")
[1] \"Hello--World\"

where the argument collapse specifies the character(s) to be used between the elements of the vector to be collapsed.

You can even combine both:

> paste(x, \"and some more\", sep=\"|-|\", collapse=\"--\")
[1] \"Hello|-|and some more--World|-|and some more\"

Hope this helps.

回答2:

help.search() is a handy function, e.g.

> help.search(\"concatenate\")

will lead you to paste().

回答3:

For the first non-paste() answer, we can look at stringr::str_c() (and then toString() below). It hasn\'t been around as long as this question, so I think it\'s useful to mention that it also exists.

Very simple to use, as you can see.

tmp <- cbind(\"GAD\", \"AB\")
library(stringr)
str_c(tmp, collapse = \",\")
# [1] \"GAD,AB\"

From its documentation file description, it fits this problem nicely.

To understand how str_c works, you need to imagine that you are building up a matrix of strings. Each input argument forms a column, and is expanded to the length of the longest argument, using the usual recyling rules. The sep string is inserted between each column. If collapse is NULL each row is collapsed into a single string. If non-NULL that string is inserted at the end of each row, and the entire matrix collapsed to a single string.

Added 4/13/2016: It\'s not exactly the same as your desired output (extra space), but no one has mentioned it either. toString() is basically a version of paste() with collapse = \", \" hard-coded, so you can do

toString(tmp)
# [1] \"GAD, AB\"

回答4:

> tmp = paste(\"GAD\", \"AB\", sep = \",\")
> tmp
[1] \"GAD,AB\"

I found this from Google by searching for R concatenate strings: http://stat.ethz.ch/R-manual/R-patched/library/base/html/paste.html

回答5:

Alternatively, if your objective is to output directly to a file or stdout, you can use cat:

cat(s1, s2, sep=\", \")

回答6:

As others have pointed out, paste() is the way to go. But it can get annoying to have to type paste(str1, str2, str3, sep=\'\') everytime you want the non-default separator.

You can very easily create wrapper functions that make life much simpler. For instance, if you find yourself concatenating strings with no separator really often, you can do:

p <- function(..., sep=\'\') {
    paste(..., sep=sep, collapse=sep)
}

or if you often want to join strings from a vector (like implode() from PHP):

implode <- function(..., sep=\'\') {
     paste(..., collapse=sep)
}

Allows you do do this:

p(\'a\', \'b\', \'c\')
#[1] \"abc\"
vec <- c(\'a\', \'b\', \'c\')
implode(vec)
#[1] \"abc\"
implode(vec, sep=\', \')
#[1] \"a, b, c\"

Also, there is the built-in paste0, which does the same thing as my implode, but without allowing custom separators. It\'s slightly more efficient than paste().

回答7:

You can create you own operator :

\'%&%\' <- function(x, y)paste0(x,y)
\"new\" %&% \"operator\"
[1] newoperator`

You can also redefine \'and\' (&) operator :

\'&\' <- function(x, y)paste0(x,y)
\"dirty\" & \"trick\"
\"dirtytrick\"

messing with baseline syntax is ugly, but so is using paste()/paste0() if you work only with your own code you can (almost always) replace logical & and operator with * and do multiplication of logical values instead of using logical \'and &\'

回答8:

Another way:

sprintf(\"%s you can add other static strings here %s\",string1,string2)

It sometimes useful than paste() function. %s denotes the place where the subjective strings will be included.

Note that this will come in handy as you try to build a path:

sprintf(\"/%s\", paste(\"this\", \"is\", \"a\", \"path\", sep=\"/\"))

output

/this/is/a/path

回答9:

Given the matrix, tmp, that you created:

paste(tmp[1,], collapse = \",\")

I assume there is some reason why you\'re creating a matrix using cbind, as opposed to simply:

tmp <- \"GAD,AB\"

回答10:

Consider the case where the strings are columns and the result should be a new column:

df <- data.frame(a = letters[1:5], b = LETTERS[1:5], c = 1:5)

df$new_col <- do.call(paste, c(df[c(\"a\", \"b\")], sep = \", \")) 
df
#  a b c new_col
#1 a A 1    a, A
#2 b B 2    b, B
#3 c C 3    c, C
#4 d D 4    d, D
#5 e E 5    e, E

Optionally, skip the [c(\"a\", \"b\")] subsetting if all columns needs to be pasted.

# you can also try str_c from stringr package as mentioned by other users too!
do.call(str_c, c(df[c(\"a\", \"b\")], sep = \", \")) 

回答11:

Another non-paste answer:

x <- capture.output(cat(data, sep = \",\"))
x
[1] \"GAD,AB\"

Where

 data <- c(\"GAD\", \"AB\")