Fast algorithm for extracting a subset of lines from a string
MIT License
Very efficient module for extracting a subset of lines from a string.
Similar to str.slice(beginIndex, endIndex)
except that the indexes are
lines instead of bytes.
npm install slice-lines --save
const sliceLines = require('slice-lines')
const text = 'first line\n2nd line\r\nlast line'
sliceLines(text, 1) // => "2nd line\r\nlast line"
sliceLines(text, 1, 2) // => "2nd line"
sliceLines(text, 0, 2) // => "first line\n2nd line"
sliceLines(text, -1)) // => "last line"
lines = sliceLines(str, beginIndex[, endIndex])
Returns a string containing the requested lines.
Arguments:
str
- The string to extract lines frombeginIndex
- The zero-based line index at which to begin extraction.totalLines + beginIndex
wheretotalLines
is the total number of lines in str
(for example, ifbeginIndex
is -3
it is treated as totalLines - 3
). IfbeginIndex
is greater than or equal to the total number of lines insliceLines()
returns an empty stringendIndex
- Optional. The zero-based line index before which to endendIndex
sliceLines()
extracts to the end of the string. IftotalLines + endIndex
where totalLines
str
(for example, if endIndex
is-3
it is treated as totalLines - 3
)The classic way of extracting a specific line from a text in JavaScript
is using str.split()
with either \n
as the separator or the even
slower regex /\r?\n/
if support for Windows line-breaks are required.
That approach requires a complete traversal of the entire text + contruction of new objects and strings for each line in the text.
As seen below sliceLines()
can be several orders of magnitudes faster
and isn't impacted by the size of the text.
Example extracting a line from a text with 500,000 lines
# sliceLines(str, 0, 1) // V8 unoptimized
ok ~1.19 ms (0 s + 1189464 ns)
# sliceLines(str, 0, 1) // V8 optimized
ok ~258 μs (0 s + 258238 ns)
# sliceLines(str, 10000, 10001)
ok ~406 μs (0 s + 406363 ns)
# sliceLines(str, -1) // last line relative
ok ~26 ms (0 s + 25749953 ns)
# sliceLines(str, 499999) // last line by index
ok ~15 ms (0 s + 14732301 ns)
# str.split('\n')[10000]
ok ~120 ms (0 s + 119909150 ns)
# str.split(/\r?\n/)[10000]
ok ~175 ms (0 s + 174632829 ns)
MIT