Create a Vec <BTreeSet <char>> from Vec <Vec <char>>

Question

I am trying to create a set ( Vec<BTreeSet<char>>) vector from Vec<Vec<char>>. Here is my progress:

use std::collections::BTreeSet;

fn main() {
    // The data
    let transaction_list = [
        vec!['A','B','C','D'],
        vec!['B','B','C'],
        vec!['A','B','B','D']
    ];

    // Successfully created a set from the Vec of Vec. It contains unique chars
    let item_set: BTreeSet<char> = transaction_list.iter().flat_map(|t| t).cloned().collect();

    // Made the same Vec of Vec. Basically just experimenting with map and collect
    let the_same_transaction_list: Vec<Vec<char>> = transaction_list.iter().map(|t| t ).cloned().collect::<Vec<_>>();

    // ERROR
    let transaction_set: Vec<BTreeSet<char>> = transaction_list
                                                .iter()
                                                .map(|t| t.iter().map(|t| t).cloned().collect() )
                                                .cloned().collect::<Vec<_>>();
}

Error message:

error: the trait `core::iter::FromIterator<char>` is not implemented for the type `&_` [E0277]
                                      .map(|t| t.iter().map(|t| t).cloned().collect() )
                                                                            ^~~~~~~~~
help: see the detailed explanation for E0277
note: a collection of type `&_` cannot be built from an iterator over elements of type `char`

I did not find the right way to make Vec<BTreeSet<char>>out Vec<Vec<char>>. Here's the url of the playground: http://is.gd/WVONHY .

Answer 1

The error message is a bit odd. Here's the solution:

let transaction_set: Vec<BTreeSet<_>> =
    transaction_list
    .iter()
    .map(|t| t.iter().cloned().collect())
    .collect();

Two major changes:

• map(|x| x)pointless. This is a no-op.
• I deleted the external one cloned. The type of call result mapwill already be BTreeSet. There is no need then to clone it again.

, :

fn cloned<'a, T>(self) -> Cloned<Self> 
    where Self: Iterator<Item=&'a T>,
          T: 'a + Clone

cloned, Item , . BTreeSet s, . , collect char &_ ( - ), cloned. , , , collect. , :

let transaction_set: Vec<_> =
    transaction_list
    .iter()
    .map(|t| -> BTreeSet<_> {t.iter().cloned().collect()})
    .cloned().collect();

:

error: type mismatch resolving `<[closure...] as core::ops::FnOnce<(&collections::vec::Vec<char>,)>>::Output == &_`:
 expected struct `collections::btree::set::BTreeSet`,
    found &-ptr [E0271]
         .cloned().collect();
          ^~~~~~~~

error: no method named `collect` found for type `core::iter::Cloned<core::iter::Map<core::slice::Iter<'_, collections::vec::Vec<char>>, [closure...]>>` in the current scope
         .cloned().collect();
                   ^~~~~~~~~
note: the method `collect` exists but the following trait bounds were not satisfied: `core::iter::Cloned<core::iter::Map<core::slice::Iter<'_, collections::vec::Vec<char>>, [closure...]>> : core::iter::Iterator`

, - cloned.