langref.org - python, fsharp, fantom, groovy ... - Lists | Output | From a List Produce a List of Duplicate Entries

View Problem

Lists

Output

From a List Produce a List of Duplicate Entries

Taking a list:
["andrew", "bob", "chris", "bob"]

Write the code to produce a list of duplicates in the list:
["bob"]

python 2.4

import itertools
input = ["andrew", "bob", "chris", "bob"]
input.sort()
output = [k for k, g in itertools.groupby(input, lambda x: x) if len(list(g)) > 1]

fsharp

["andrew"; "bob"; "chris"; "bob"]
|> Seq.countBy id
|> Seq.filter (fun (k,n) -> n > 1)
|> Seq.map fst
|> Seq.toList

fantom

nameCounts := Str:Int[:] { def = 0 }
["andrew", "bob", "chris", "bob"].each |Str v| { nameCounts[v]++ }
results := nameCounts.findAll |Int v, Str k->Bool| { v > 1 }.keys
echo(results.join(","))

groovy 1.7.6

def input = ["andrew", "bob", "chris", "bob"]

def output = input.findAll{input.count(it)>1}.unique()

assert output == ["bob"]

haskell

import Data.List

input = ["andrew", "bob", "chris", "bob"]
output = [ head l | l <- group (sort input), length l > 1]

cpp C++0x/C++11 (gcc >=4.6)

vector<string> lst = { "andrew", "bob", "chris", "bob" };
vector<string> lst_no_dups;
vector<string> tmp;
vector<string> dups;

sort(lst.begin(), lst.end());
unique_copy(lst.begin(), lst.end(), back_inserter(lst_no_dups));
set_difference(lst.begin(), lst.end(),
lst_no_dups.begin(), lst_no_dups.end(),
back_inserter(tmp));
unique_copy(tmp.begin(), tmp.end(), back_inserter(dups));

cout << dups << endl;

cpp C++0x/C++11 (gcc >=4.6)

list<string> lst = { "andrew", "bob", "chris", "bob" };
map<string,int> num_identical;
list<string> dups;

for (auto &s: lst)
num_identical[s]++;
for (auto &n: num_identical)
if (n.second > 1)
dups.push_back(n.first);
cout << dups << endl;

Submit a new solution for python, fsharp, fantom, groovy ...
There are 14 other solutions in additional languages (clojure, csharp, erlang, java ...)