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[英]Vec<&str>` cannot be built from an iterator over elements of type ()
[英]Trying to collect into vector but failing with “a collection cannot be built over elements of type <…>”
我试图找到矩阵的鞍点,借来的向量数组。 为此,鞍点是矩阵中的元素,该元素在其列中最小,在其行中最大,或者在其列中最大,在其行中最小。
use rayon::prelude::*;
pub fn find_saddle_points(input: &[Vec<u64>]) -> Vec<(usize, usize)> {
let flattened_matrix: Vec<(&u64)> = input.into_par_iter().flatten().collect::<Vec<&u64>>();
match flattened_matrix == vec![] { //Check for empty input
true => vec![],
false => {
let num_rows: usize = input.len();
let num_cols: usize = input[0].len();
let row_minima: Vec<Option<&u64>> = (0_usize..(num_rows - 1_usize))
.into_par_iter()
.map(|row_index| input[row_index].iter().min())
.collect::<Vec<Option<&u64>>>();
let row_maxima: Vec<Option<&u64>> = (0_usize..(num_rows - 1_usize))
.into_par_iter()
.map(|row_index| input[row_index].iter().max())
.collect::<Vec<Option<&u64>>>();
let input_tranpose: Vec<Vec<u64>> = (0_usize..(num_cols - 1_usize)) //Transpose the matrix to make it easier to get column information
.into_par_iter()
.map(|col_index| {
(0_usize..(num_rows - 1_usize))
.map(|row_index| input[row_index][col_index])
.collect::<Vec<u64>>() //Individual column
})
.collect::<Vec<Vec<u64>>>();
let col_minima: Vec<Option<&u64>> = (0_usize..(num_cols - 1_usize))
.into_par_iter()
.map(|col_index| input_tranpose[col_index].iter().min())
.collect::<Vec<Option<&u64>>>();
let col_maxima: Vec<Option<&u64>> = (0_usize..(num_cols - 1_usize))
.into_par_iter()
.map(|col_index| input_tranpose[col_index].iter().max())
.collect::<Vec<Option<&u64>>>();
//All fine up to this point
(0_usize..(num_rows - 1_usize))
.map(|row_index| {
(0_usize..(num_cols - 1_usize)).map(|col_index| {
match (Some(row_minima[row_index]) == Some(col_maxima[col_index])
|| Some(row_maxima[row_index]) == Some(col_minima[col_index]))
{
true => Some((row_index, col_index)),
false => None,
}
})
})
.collect::<Vec<(usize, usize)>>()
}
}
}
错误在最终的.collect
:
error[E0277]: a collection of type `std::vec::Vec<(usize, usize)>` cannot be built from an iterator over elements of type `std::iter::Map<std::ops::Range<usize>, [closure@src/lib.rs:45:57: 52:22 row_minima:_, row_index:_, col_maxima:_, row_maxima:_, col_minima:_]>`
--> src/lib.rs:54:18
|
54 | .collect::<Vec<(usize, usize)>>()
| ^^^^^^^ a collection of type `std::vec::Vec<(usize, usize)>` cannot be built from `std::iter::Iterator<Item=std::iter::Map<std::ops::Range<usize>, [closure@src/lib.rs:45:57: 52:22 row_minima:_, row_index:_, col_maxima:_, row_maxima:_, col_minima:_]>>`
|
= help: the trait `std::iter::FromIterator<std::iter::Map<std::ops::Range<usize>, [closure@src/lib.rs:45:57: 52:22 row_minima:_, row_index:_, col_maxima:_, row_maxima:_, col_minima:_]>>` is not implemented for `std::vec::Vec<(usize, usize)>`
我知道这是由于迭代器受到了不属于期望类型的collect
函数引起的,但是对我来说这应该是正确的,并且我不清楚为什么不是这样。
( 聊天记录会指导您完成该问题的解决方案,因为它很复杂)
TL; DR使用Iterator::flat_map
和Iterator::filter_map
来解决此问题。
(0_usize..(num_rows - 1_usize))
.flat_map(|row_index| {
(0_usize..(num_cols - 1_usize)).flat_map(|col_index| {
match row_minima[row_index] == col_maxima[col_index]
|| row_maxima[row_index] == col_minima[col_index]
{
true => Some((row_index, col_index)),
false => None,
}
})
})
.collect::<Vec<(usize, usize)>>()
请注意,该代码非常简单,但是显示了解决方案。
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