Splitting and Joining

Part of the Logic & Flow section of Coddy's R journey. Lesson 3 of 64.

strsplit(x, split) cuts a string at every separator. It returns a list with one character vector per input string, so take [[1]] to get the pieces of a single string.

csv <- "red,green,blue"
parts <- strsplit(csv, ",")[[1]]
print(parts)
print(length(parts))

Output:

[1] "red"   "green" "blue" 
[1] 3

paste() goes the other way. With collapse, it joins the elements of one vector into a single string with the collapse text between them. sep goes between the arguments, element by element.

words <- c("one", "two", "three")
print(paste(words, collapse = "-"))
print(paste(words, 1:3, sep = "_"))

Output:

[1] "one-two-three"
[1] "one_1"   "two_2"   "three_3"

Text from input often has spaces around the separators. trimws() removes the spaces at the start and end of each element:

raw <- "  apples , pears,plums  "
items <- trimws(strsplit(raw, ",")[[1]])
print(items)
print(paste(rev(items), collapse = " | "))

Output:

[1] "apples" "pears"  "plums" 
[1] "plums | pears | apples"

strsplit() on a vector returns one list element per string, so each input line keeps its own pieces:

lines <- c("a,b", "c,d,e")
parts <- strsplit(lines, ",")
print(length(parts))
print(parts[[2]])

Output:

[1] 2
[1] "c" "d" "e"

Challenge

Easy

Complete hashtags(line). The line holds tags separated by commas, possibly with spaces around them. Return one string with every tag prefixed by #, separated by single spaces: r, data ,stats becomes #r #data #stats.

The supplied code reads the line and prints the returned value.

Try it yourself

hashtags <- function(line) {
  # Write your code here
  line
}

# Supplied input/output code: keep it as it is
input <- suppressWarnings(readLines(file("stdin")))
cat(hashtags(input[1]), sep = "\n")