Could someone help me to write a function that checks if a string is a substring of another string?
(there can be more than only 2 strings)
Thanks
With String module:
let contains s1 s2 =
try
let len = String.length s2 in
for i = 0 to String.length s1 - len do
if String.sub s1 i len = s2 then raise Exit
done;
false
with Exit -> true
With Str module, like #barti_ddu said check this topic:
let contains s1 s2 =
let re = Str.regexp_string s2 in
try
ignore (Str.search_forward re s1 0);
true
with Not_found -> false
With Batteries, you can use String.exists. It also exists in ExtLib: String.exists.
A String-based alternative to cago's answer that might have better performance and lower memory usage:
let is_substring string substring =
let ssl = String.length substring and sl = String.length string in
if ssl = 0 || ssl > sl then false else
let max = sl - ssl and clone = String.create ssl in
let rec check pos =
pos <= max && (
String.blit string pos clone 0 ssl ; clone = substring
|| check (String.index_from string (succ pos) substring.[0])
)
in
try check (String.index string substring.[0])
with Not_found -> false
String str="hello world";
System.out.println(str.contains("world"));//true
System.out.println(str.contains("world1"));//false
Related
How to count a character occurrence in string in Nim, mainly using its native statements prior go to module ? eg.
var
str = "Hello World"
c : int
c = numChar( "o", str ) # <- illustration only ?
The earlier answer is correct but if you do not want to import any modules you can write your own procedure:
proc count_char(value: string = "Hello World", ch: char = 'o'): int =
var cnt_c: int = 0
for c in value:
if c == ch:
cnt_c += 1
result = cnt_c
var
val: string = "Mother Goose"
ch: char = 'o'
echo $count_char(val, ch)
PS: Unrelated - Need syntax highlight for nim-lang on SO.
Use the count function from strutils:
import std/strutils
let str = "Hello World"
let count = count(str, 'o')
assert count = 1
There’s also a string overload for counting sub strings as well.
I have a string "PIXEL STUDIOS - TEST1" My code works until I reach the first space in the string.
var str = label.stringValue
let c = str.characters
let r = c.index(c.startIndex, offsetBy: 6)..<c.index(c.endIndex, offsetBy: 0)
let substring = str[r]
print(substring)
When I run my code and offsetBy 5 it works but when I try to offset past that point I get the error. Is there something else I need to do to handle spaces in my string?
Your code is working with the given string:
var str = "PIXEL STUDIOS - TEST1"
let c = str.characters
let r = c.index(c.startIndex, offsetBy: 6)..<c.index(c.endIndex, offsetBy: 0)
let substring = str[r]
print(substring)
prints:
STUDIOS - TEST1
Conclusion: label.stringValue is fishy.
Print it out for further investigations.
I want to read a line from a file, initialize an array from that line and then display the integers.
Why is is not reading the five integers in the line? I want to get output 1 2 3 4 5, i have 1 1 1 1 1
open Array;;
open Scanf;;
let print_ints file_name =
let file = open_in file_name in
let s = input_line(file) in
let n = ref 5 in
let arr = Array.init !n (fun i -> if i < !n then sscanf s "%d" (fun a -> a) else 0) in
let i = ref 0 in
while !i < !n do
print_int (Array.get arr !i);
print_string " ";
i := !i + 1;
done;;
print_ints "string_ints.txt";;
My file is just: 1 2 3 4 5
You might want to try the following approach. Split your string into a list of substrings representing numbers. This answer describes one way of doing so. Then use the resulting function in your print_ints function.
let ints_of_string s =
List.map int_of_string (Str.split (Str.regexp " +") s)
let print_ints file_name =
let file = open_in file_name in
let s = input_line file in
let ints = ints_of_string s in
List.iter (fun i -> print_int i; print_char ' ') ints;
close_in file
let _ = print_ints "string_ints.txt"
When compiling, pass str.cma or str.cmxa as an argument (see this answer for details on compilation):
$ ocamlc str.cma print_ints.ml
Another alternative would be using the Scanf.bscanf function -- this question, contains an example (use with caution).
The Scanf.sscanf function may not be particularly suitable for this task.
An excerpt from the OCaml manual:
the scanf facility is not intended for heavy duty lexical analysis and parsing. If it appears not expressive enough for your needs, several alternative exists: regular expressions (module Str), stream parsers, ocamllex-generated lexers, ocamlyacc-generated parsers
There is though a way to parse a string of ints using Scanf.sscanf (which I wouldn't recommend):
let rec int_list_of_string s =
try
Scanf.sscanf s
"%d %[0-9-+ ]"
(fun n rest_str -> n :: int_list_of_string rest_str)
with
| End_of_file | Scanf.Scan_failure _ -> []
The trick here is to represent the input string s as a part which is going to be parsed into a an integer (%d) and the rest of the string using the range format: %[0-9-+ ]", which will match the rest of the string, containing only decimal digits 0-9, the - and + signs, and whitespace .
I want the last character from a string
I've got str.[str.Length - 1], but that's ugly. There must be a better way.
There's no better way to do it - what you have is fine.
If you really plan to do it a lot, you can author an F# extension property on the string type:
let s = "food"
type System.String with
member this.Last =
this.Chars(this.Length-1) // may raise an exception
printfn "%c" s.Last
This could be also handy:
let s = "I am string"
let lastChar = s |> Seq.last
Result:
val lastChar : char = 'g'
(This is old question), someone might find this useful, orig answer from Brian.
type System.String with
member this.Last() =
if this.Length > 1 then
this.Chars(this.Length - 1).ToString()
else
this.[0].ToString()
member this.Last(n:int) =
let absn = Math.Abs(n)
if this.Length > absn then
let nn =
let a = if absn = 0 then 1 else absn
let b = this.Length - a
if b < 0 then 0 else b
this.Chars(nn).ToString()
else
this.[0].ToString()
"ABCD".Last() -> "D"
"ABCD".Last(1) -> "D"
"ABCD".Last(-1) -> "D"
"ABCD".Last(2) -> "C"
You could also treat it as a sequence, but I'm not sure if that's any more or less ugly than the solution you have:
Seq.nth (Seq.length str - 1) str
To learn the basics of OCaml, I'm solving one of the easy facebook engineering puzzles using it. Essentially, I'd like to do something like the following Python code:
some_str = some_str.strip()
That is, I'd like to strip all of the whitespace from the beginning and the end. I don't see anything obvious to do this in the OCaml Str library. Is there any easy way to do this, or am I going to have to write some code to do it (which I wouldn't mind, but would prefer not to :) ).
Bear in mind that I'm limited to what's in the libraries that come with the OCaml distribution.
I know this question is uber-old, but I was just pondering the same thing and came-up with this (from toplevel):
let strip str =
let str = Str.replace_first (Str.regexp "^ +") "" str in
Str.replace_first (Str.regexp " +$") "" str;;
val strip : string -> string = <fun>
then
strip " Hello, world! ";;
- : string = "Hello, world!"
UPDATE:
As of 4.00.0, standard library includes String.trim
It is really a mistake to limit yourself to the standard library, since the standard ilbrary is missing a lot of things. If, for example, you were to use Core, you could simply do:
open Core.Std
let x = String.strip " foobar "
let () = assert (x = "foobar")
You can of course look at the sources of Core if you want to see the implementation. There is a similar function in ExtLib.
how about
let trim str =
if str = "" then "" else
let search_pos init p next =
let rec search i =
if p i then raise(Failure "empty") else
match str.[i] with
| ' ' | '\n' | '\r' | '\t' -> search (next i)
| _ -> i
in
search init
in
let len = String.length str in
try
let left = search_pos 0 (fun i -> i >= len) (succ)
and right = search_pos (len - 1) (fun i -> i < 0) (pred)
in
String.sub str left (right - left + 1)
with
| Failure "empty" -> ""
(Via Code Codex)
I believe at the point when the other answers were given, version 4.00 was not out yet. Actually, in OCaml 4.00, there is a String.trim function in the string module to trim leading and trailing white spaces.
Alternatively, if you're restricted to an older version of OCaml, you may use this function that is shamelessly copied from the source of 4.00's string module.
let trim s =
let is_space = function
| ' ' | '\012' | '\n' | '\r' | '\t' -> true
| _ -> false in
let len = String.length s in
let i = ref 0 in
while !i < len && is_space (String.get s !i) do
incr i
done;
let j = ref (len - 1) in
while !j >= !i && is_space (String.get s !j) do
decr j
done;
if !i = 0 && !j = len - 1 then
s
else if !j >= !i then
String.sub s !i (!j - !i + 1)
else
""
;;
Something simple like this should work fine:
#require "str";;
let strip_string s =
Str.global_replace (Str.regexp "[\r\n\t ]") "" s
Standard library's
String.trim
does exactly that.