Find Unique Characters in a File - search

Question

I have a file with 450,000+ rows of entries. Each entry is about 7 characters in length. What I want to know is the unique characters of this file.
For instance, if my file were the following;
Entry
-----
Yabba
Dabba
Doo
Then the result would be
Unique characters: {abdoy}
Notice I don't care about case and don't need to order the results. Something tells me this is very easy for the Linux folks to solve.
Update
I'm looking for a very fast solution. I really don't want to have to create code to loop over each entry, loop through each character...and so on. I'm looking for a nice script solution.
Update 2
By Fast, I mean fast to implement...not necessarily fast to run.

Answer 1

BASH shell script version (no sed/awk):
while read -n 1 char; do echo "$char"; done < entry.txt | tr [A-Z] [a-z] | sort -u
UPDATE: Just for the heck of it, since I was bored and still thinking about this problem, here's a C++ version using set. If run time is important this would be my recommended option, since the C++ version takes slightly more than half a second to process a file with 450,000+ entries.
#include <iostream>
#include <set>
int main() {
std::set<char> seen_chars;
std::set<char>::const_iterator iter;
char ch;
/* ignore whitespace and case */
while ( std::cin.get(ch) ) {
if (! isspace(ch) ) {
seen_chars.insert(tolower(ch));
}
}
for( iter = seen_chars.begin(); iter != seen_chars.end(); ++iter ) {
std::cout << *iter << std::endl;
}
return 0;
}
Note that I'm ignoring whitespace and it's case insensitive as requested.
For a 450,000+ entry file (chars.txt), here's a sample run time:
[user#host]$ g++ -o unique_chars unique_chars.cpp
[user#host]$ time ./unique_chars < chars.txt
a
b
d
o
y
real 0m0.638s
user 0m0.612s
sys 0m0.017s

Answer 2

As requested, a pure shell-script "solution":
sed -e "s/./\0\n/g" inputfile | sort -u
It's not nice, it's not fast and the output is not exactly as specified, but it should work ... mostly.
For even more ridiculousness, I present the version that dumps the output on one line:
sed -e "s/./\0\n/g" inputfile | sort -u | while read c; do echo -n "$c" ; done

Answer 3

Use a set data structure. Most programming languages / standard libraries come with one flavour or another. If they don't, use a hash table (or generally, dictionary) implementation and just omit the value field. Use your characters as keys. These data structures generally filter out duplicate entries (hence the name set, from its mathematical usage: sets don't have a particular order and only unique values).

Answer 4

Quick and dirty C program that's blazingly fast:
#include <stdio.h>
int main(void)
{
int chars[256] = {0}, c;
while((c = getchar()) != EOF)
chars[c] = 1;
for(c = 32; c < 127; c++) // printable chars only
{
if(chars[c])
putchar(c);
}
putchar('\n');
return 0;
}
Compile it, then do
cat file | ./a.out
To get a list of the unique printable characters in file.

Answer 5

Python w/sets (quick and dirty)
s = open("data.txt", "r").read()
print "Unique Characters: {%s}" % ''.join(set(s))
Python w/sets (with nicer output)
import re
text = open("data.txt", "r").read().lower()
unique = re.sub('\W, '', ''.join(set(text))) # Ignore non-alphanumeric
print "Unique Characters: {%s}" % unique

Answer 6

Here's a PowerShell example:
gc file.txt | select -Skip 2 | % { $_.ToCharArray() } | sort -CaseSensitive -Unique
which produces:
D
Y
a
b
o
I like that it's easy to read.
EDIT: Here's a faster version:
$letters = #{} ; gc file.txt | select -Skip 2 | % { $_.ToCharArray() } | % { $letters[$_] = $true } ; $letters.Keys

Answer 7

A very fast solution would be to make a small C program that reads its standard input, does the aggregation and spits out the result.
Why the arbitrary limitation that you need a "script" that does it?
What exactly is a script anyway?
Would Python do?
If so, then this is one solution:
import sys;
s = set([]);
while True:
line = sys.stdin.readline();
if not line:
break;
line = line.rstrip();
for c in line.lower():
s.add(c);
print("".join(sorted(s)));

Answer 8

Algorithm:
Slurp the file into memory.
Create an array of unsigned ints, initialized to zero.
Iterate though the in memory file, using each byte as a subscript into the array.
increment that array element.
Discard the in memory file
Iterate the array of unsigned int
if the count is not zero,
display the character, and its corresponding count.

Answer 9

cat yourfile |
perl -e 'while(<>){chomp;$k{$_}++ for split(//, lc $_)}print keys %k,"\n";'

Answer 10

Alternative solution using bash:
sed "s/./\l\0\n/g" inputfile | sort -u | grep -vc ^$
EDIT Sorry, I actually misread the question. The above code counts the unique characters. Just omitting the c switch at the end obviously does the trick but then, this solution has no real advantage to saua's (especially since he now uses the same sed pattern instead of explicit captures).

Answer 11

While not an script this java program will do the work. It's easy to understand an fast ( to run )
import java.util.*;
import java.io.*;
public class Unique {
public static void main( String [] args ) throws IOException {
int c = 0;
Set s = new TreeSet();
while( ( c = System.in.read() ) > 0 ) {
s.add( Character.toLowerCase((char)c));
}
System.out.println( "Unique characters:" + s );
}
}
You'll invoke it like this:
type yourFile | java Unique
or
cat yourFile | java Unique
For instance, the unique characters in the HTML of this question are:
Unique characters:[ , , , , !, ", #, $, %, &, ', (, ), +, ,, -, ., /, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, :, ;, <, =, >, ?, #, [, \, ], ^, _, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z, {, |, }]

Answer 12

Print unique characters (ASCII and Unicode UTF-8)
import codecs
file = codecs.open('my_file_name', encoding='utf-8')
# Runtime: O(1)
letters = set()
# Runtime: O(n^2)
for line in file:
for character in line:
letters.add(character)
# Runtime: O(n)
letter_str = ''.join(letters)
print(letter_str)
Save as unique.py, and run as python unique.py.

Answer 13

in c++ i would first loop through the letters in the alphabet then run a strchr() on each with the file as a string. this will tell you if that letter exists, then just add it to the list.

Answer 14

Try this file with JSDB Javascript (includes the javascript engine in the Firefox browser):
var seenAlreadyMap={};
var seenAlreadyArray=[];
while (!system.stdin.eof)
{
var L = system.stdin.readLine();
for (var i = L.length; i-- > 0; )
{
var c = L[i].toLowerCase();
if (!(c in seenAlreadyMap))
{
seenAlreadyMap[c] = true;
seenAlreadyArray.push(c);
}
}
}
system.stdout.writeln(seenAlreadyArray.sort().join(''));

Answer 15

Python using a dictionary. I don't know why people are so tied to sets or lists to hold stuff. Granted a set is probably more efficient than a dictionary. However both are supposed to take constant time to access items. And both run circles around a list where for each character you search the list to see if the character is already in the list or not. Also Lists and Dictionaries are built in Python datatatypes that everyone should be using all the time. So even if set doesn't come to mind, dictionary should.
file = open('location.txt', 'r')
letters = {}
for line in file:
if line == "":
break
for character in line.strip():
if character not in letters:
letters[character] = True
file.close()
print "Unique Characters: {" + "".join(letters.keys()) + "}"

Answer 16

A C solution. Admittedly it is not the fastest to code solution in the world. But since it is already coded and can be cut and pasted, I think it counts as "fast to implement" for the poster :) I didn't actually see any C solutions so I wanted to post one for the pure sadistic pleasure :)
#include<stdio.h>
#define CHARSINSET 256
#define FILENAME "location.txt"
char buf[CHARSINSET + 1];
char *getUniqueCharacters(int *charactersInFile) {
int x;
char *bufptr = buf;
for (x = 0; x< CHARSINSET;x++) {
if (charactersInFile[x] > 0)
*bufptr++ = (char)x;
}
bufptr = '\0';
return buf;
}
int main() {
FILE *fp;
char c;
int *charactersInFile = calloc(sizeof(int), CHARSINSET);
if (NULL == (fp = fopen(FILENAME, "rt"))) {
printf ("File not found.\n");
return 1;
}
while(1) {
c = getc(fp);
if (c == EOF) {
break;
}
if (c != '\n' && c != '\r')
charactersInFile[c]++;
}
fclose(fp);
printf("Unique characters: {%s}\n", getUniqueCharacters(charactersInFile));
return 0;
}

Answer 17

Quick and dirty solution using grep (assuming the file name is "file"):
for char in a b c d e f g h i j k l m n o p q r s t u v w x y z; do
if [ ! -z "`grep -li $char file`" ]; then
echo -n $char;
fi;
done;
echo
I could have made it a one-liner but just want to make it easier to read.
(EDIT: forgot the -i switch to grep)

Answer 18

Well my friend, I think this is what you had in mind....At least this is the python version!!!
f = open("location.txt", "r") # open file
ll = sorted(list(f.read().lower())) #Read file into memory, split into individual characters, sort list
ll = [val for idx, val in enumerate(ll) if (idx == 0 or val != ll[idx-1])] # eliminate duplicates
f.close()
print "Unique Characters: {%s}" % "".join(ll) #print list of characters, carriage return will throw in a return
It does not iterate through each character, it is relatively short as well. You wouldn't want to open a 500 MB file with it (depending upon your RAM) but for shorter files it is fun :)
I also have to add my final attack!!!! Admittedly I eliminated two lines by using standard input instead of a file, I also reduced the active code from 3 lines to 2. Basically if I replaced ll in the print line with the expression from the line above it, I could have had 1 line of active code and one line of imports.....Anyway now we are having fun :)
import itertools, sys
# read standard input into memory, split into characters, eliminate duplicates
ll = map(lambda x:x[0], itertools.groupby(sorted(list(sys.stdin.read().lower()))))
print "Unique Characters: {%s}" % "".join(ll) #print list of characters, carriage return will throw in a return

Answer 19

This answer above mentioned using a dictionary.
If so, the code presented there can be streamlined a bit, since the Python documentation states:
It is best to think of a dictionary as
an unordered set of key: value pairs,
with the requirement that the keys are
unique (within one dictionary).... If
you store using a key that is already
in use, the old value associated with
that key is forgotten.
Therefore, this line of the code can be removed, since the dictionary keys will always be unique anyway:
if character not in letters:
And that should make it a little faster.

Answer 20

Where C:/data.txt contains 454,863 rows of seven random alphabetic characters, the following code
using System;
using System.IO;
using System.Collections;
using System.Diagnostics;
namespace ConsoleApplication {
class Program {
static void Main(string[] args) {
FileInfo fileInfo = new FileInfo(#"C:/data.txt");
Console.WriteLine(fileInfo.Length);
Stopwatch sw = new Stopwatch();
sw.Start();
Hashtable table = new Hashtable();
StreamReader sr = new StreamReader(#"C:/data.txt");
while (!sr.EndOfStream) {
char c = Char.ToLower((char)sr.Read());
if (!table.Contains(c)) {
table.Add(c, null);
}
}
sr.Close();
foreach (char c in table.Keys) {
Console.Write(c);
}
Console.WriteLine();
sw.Stop();
Console.WriteLine(sw.ElapsedMilliseconds);
}
}
}
produces output
4093767
mytojevqlgbxsnidhzupkfawr
c
889
Press any key to continue . . .
The first line of output tells you the number of bytes in C:/data.txt (454,863 * (7 + 2) = 4,093,767 bytes). The next two lines of output are the unique characters in C:/data.txt (including a newline). The last line of output tells you the number of milliseconds the code took to execute on a 2.80 GHz Pentium 4.

Answer 21

s=open("text.txt","r").read()
l= len(s)
unique ={}
for i in range(l):
if unique.has_key(s[i]):
unique[s[i]]=unique[s[i]]+1
else:
unique[s[i]]=1
print unique

Answer 22

Python without using a set.
file = open('location', 'r')
letters = []
for line in file:
for character in line:
if character not in letters:
letters.append(character)
print(letters)

Answer 23

Old question, I know, but here's a fast solution, meaning it runs fast, and it's probably also pretty fast to code if you know how to copy/paste ;)
BACKGROUND
I had a huge csv file (12 GB, 1.34 million lines, 12.72 billion characters) that I was loading into postgres that was failing because it had some "bad" characters in it, so naturally I was trying to find a character not in that file that I could use as a quote character.
1. First try: Jay's C++ solution
I started with #jay's C++ answer:
(Note: all of these code examples were compiled with g++ -O2 uniqchars.cpp -o uniqchars)
#include <iostream>
#include <set>
int main() {
std::set<char> seen_chars;
std::set<char>::const_iterator iter;
char ch;
/* ignore whitespace and case */
while ( std::cin.get(ch) ) {
if (! isspace(ch) ) {
seen_chars.insert(tolower(ch));
}
}
for( iter = seen_chars.begin(); iter != seen_chars.end(); ++iter ) {
std::cout << *iter << std::endl;
}
return 0;
}
Timing for this one:
real 10m55.026s
user 10m51.691s
sys 0m3.329s
2. Read entire file at once
I figured it'd be more efficient to read in the entire file into memory at once, rather than all those calls to cin.get(). This reduced the run time by more than half.
(I also added a filename as a command line argument, and made it print out the characters separated by spaces instead of newlines).
#include <set>
#include <string>
#include <iostream>
#include <fstream>
#include <iterator>
int main(int argc, char **argv) {
std::set<char> seen_chars;
std::set<char>::const_iterator iter;
std::ifstream ifs(argv[1]);
ifs.seekg(0, std::ios::end);
size_t size = ifs.tellg();
fprintf(stderr, "Size of file: %lu\n", size);
std::string str(size, ' ');
ifs.seekg(0);
ifs.read(&str[0], size);
/* ignore whitespace and case */
for (char& ch : str) {
if (!isspace(ch)) {
seen_chars.insert(tolower(ch));
}
}
for(iter = seen_chars.begin(); iter != seen_chars.end(); ++iter) {
std::cout << *iter << " ";
}
std::cout << std::endl;
return 0;
}
Timing for this one:
real 4m41.910s
user 3m32.014s
sys 0m17.858s
3. Remove isspace() check and tolower()
Besides the set insert, isspace() and tolower() are the only things happening in the for loop, so I figured I'd remove them. It shaved off another 1.5 minutes.
#include <set>
#include <string>
#include <iostream>
#include <fstream>
#include <iterator>
int main(int argc, char **argv) {
std::set<char> seen_chars;
std::set<char>::const_iterator iter;
std::ifstream ifs(argv[1]);
ifs.seekg(0, std::ios::end);
size_t size = ifs.tellg();
fprintf(stderr, "Size of file: %lu\n", size);
std::string str(size, ' ');
ifs.seekg(0);
ifs.read(&str[0], size);
for (char& ch : str) {
// removed isspace() and tolower()
seen_chars.insert(ch);
}
for(iter = seen_chars.begin(); iter != seen_chars.end(); ++iter) {
std::cout << *iter << " ";
}
std::cout << std::endl;
return 0;
}
Timing for final version:
real 3m12.397s
user 2m58.771s
sys 0m13.624s

Answer 24

The simple solution from #Triptych helped me already (my input was a file of 124 MB in size, so this approach to read the entire contents into memory still worked).
However, I had a problem with encoding, python didn't interpret the UTF8 encoded input correctly. So here's a slightly modified version which works for UTF8 encoded files (and also sorts the collected characters in the output):
import io
with io.open("my-file.csv",'r',encoding='utf8') as f:
text = f.read()
print "Unique Characters: {%s}" % ''.join(sorted(set(text)))