On 2/21/20 12:51 AM, Andre Pany wrote:
Hi,
I have a 2D double array and I want to subtract from the first column a
value,
is this possible with matrix operation in D?
```
void main()
{
double[][] data = [[0.0, 1.4], [1.0, 5.2], [2.0, 0.8]];
// subtract -2.0 from the first column for every value
// Expected output
// data = [[-2.0, 1.4], [-1.0, 5.2], [0.0, 0.8]];
}
```
Kind regards
André
I don't have experience with it but mir's ndslice is designed for this:
https://github.com/libmir/mir-algorithm
Although it feels like something similar is probably already in Phobos,
I've come up with the following solution just now for fun:
import std.stdio;
import std.algorithm;
import std.range;
// At least something similar to this exists in Phobos?
struct ElementReference(R) {
ElementType!(ElementType!R) * p;
ref reference() {
return *p;
}
alias reference this;
}
struct Column(R) {
R range;
size_t n;
auto empty() {
return range.empty;
}
auto front() {
return ElementReference!R(&(range.front[n]));
}
auto popFront() {
return range.popFront();
}
}
auto byColumn(R)(R range, size_t n) {
return Column!R(range, n);
}
void main() {
double[][] data = [[0.0, 1.4], [1.0, 5.2], [2.0, 0.8]];
data.byColumn(0).each!(a => a -= 2.0);
writeln(data);
}
Ali
