Vector of vector of strings

help
1

what should be the signature of a function that returns a vector of vector of strings ?

something like :

[["one", "two", "three", "four"], ["apple", "ball", "car", "doll"], [" cat", "dog", "mouse", "lion"]]
2

It could be something like this:

fn abc() -> Vec<Vec<String>> {
    vec![vec![]]
}
3

Thanks for the reply !
I tried the same...
But i got the following error :
expected struct std::string::String, found &std::string::String

4

Try dereferencing the string and then move it into the vector (unless it's owned by another function).
Sharing your code would be helpful

let s: &String = &String::from("abc");
vec.push(*s);
5

I am trying to read data from a csv file and want to store the data in a vector of vector

This is what I wrote :

fn get_data() -> Vec<Vec<String>> {
    
    let mut rows = Vec::new();

    let mut csv_read = csv::Reader::from_reader(io::stdin());
    for line in csv_read.deserialize() {
        let mut each_row = Vec::new(); 
        let record:Record = line?;  
        for (header, value) in record.iter() {
                let v: &String = &String::from(value);
                each_row.push(*v)
            }
            rows.push(each_row)
        }
    rows
}

Then I got the following error :

let record:Record = line?;
                    ^^^^^ cannot use the `?` operator in a function that returns `std::vec::Vec<std::vec::Vec<std::string::String>>`

Can you help me in figuring this out !

6

The ? operator will check if the result of line is Ok, it it is - it will be unwrapped into record. Otherwise the Err part of the result will be returned. The problem: The function doesn't return a Result that can accept line's Err type.

Possible solutions:

  1. Use unwrap - which will cause the program to panic if a line failed to be parsed.
  2. Change the return type to Result<Vec<Vec<String>>, Error>.
7

Thank you so much !!!
Using unwrap() worked !

If I want to return csv_read directly from the above that I had written earlier, what should be the return type of the function ?

8

How to resolve the following error :

move occurs because value has type std::string::String, which does not implement the Copy trait

9

Please provide sufficient code.

2 Likes
10

You probably have something like this in the code:

let x = vec[i];

The problem is that the owned String can exist in one place only. If it's in x variable, then it can't exist in vec any more. Rust will not do magic bookkeeping for you to know where a "hole" in the vec is after the string has been moved out of it into a variable.

You can do:

let xcopy = vec[i].clone();

or

let xref = &vec[i];

to borrow the string instead of removing it from the vector.

Or if you want to remove strings from the vector, use Option<String> and .take() or vec.remove(i)/vec.swap_remove(i).

1 Like
11

Thanks for your suggestion !

12

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