arrays

问题 Is it correct to use obj.constructor === Array to test if an object is an array as suggested here? Does it always returns correct answer compatible with Array.isArray ? 回答1: Depends, there are a few scenarios where it can return a different value, but Array.isArray will work. The Array object for one window is not the the same Array object in another window. var obj = someIframe.contentWindow.someArray; console.log(obj.constructor === Array);//false console.log(Array.isArray(obj));//true The

问题 I am working on an io-ts validation where I would like to validate the list length (it has to be between min and max). I am wondering if there's a way to achieve this behavior since it could come quite handy at runtime for API endpoint validation. What I have so far is interface IMinMaxArray { readonly minMaxArray: unique symbol // use `unique symbol` here to ensure uniqueness across modules / packages } const minMaxArray = (min: number, max: number) => t.brand( t.array, (n: Array): n is t

问题 splice() mutates the original array and should be avoided. Instead, one good option is to use filter() which creates a new array so does not mutates the state. But I used to remove items from an array using splice() with spread operator. removeItem = index => { const items = [...this.state.items]; items.splice(index, 1); this.setState({ items }); } So in this case when I log items changes but this.state.items stays unchanged. Question is, why does everyone use filter instead of splice with

问题 splice() mutates the original array and should be avoided. Instead, one good option is to use filter() which creates a new array so does not mutates the state. But I used to remove items from an array using splice() with spread operator. removeItem = index => { const items = [...this.state.items]; items.splice(index, 1); this.setState({ items }); } So in this case when I log items changes but this.state.items stays unchanged. Question is, why does everyone use filter instead of splice with

问题 I am currently implementing a MINLP optimization problem in Python GEKKO for determining the optimal operational strategy of a trigeneration energy system. As I consider the energy demand during all periods of different representative days as input data, basically all my decision variables, intermediates, etc. are 2D arrays. I suspect that the declaration of the 2D intermediates is my problem. Right now I used list comprehension to declare 2D intermediates, but it seems like python cannot use

问题 So far I tried this but it returns unfiltered array: function filterRangeInPlace(array, min, max) { array = array.filter(item => (item >= min && item <= max)); console.log(array); } let arr = [5, 3, 8, 1]; filterRangeInPlace(arr, 1, 4); console.log(arr); 回答1: If it's actually important to do the filtering in-place without creating another array, you have to go sort-of old school and iterate through the array with two indexes, copying values along the way. Every time you hit an element that

问题 How can I delete one or more rows and/or columns from an array? 回答1: Working with: julia> array = [1 2 3 4; 5 6 7 8; 9 10 11 12; 13 14 15 16] 4×4 Array{Int64,2}: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 To delete a single row (here row 2): julia> newarray = array[1:end .!= 2, :] 3×4 Array{Int64,2}: 1 2 3 4 9 10 11 12 13 14 15 16 To delete a single column (here column 3): julia> newarray = array[:, 1:end .!= 3] 4×3 Array{Int64,2}: 1 2 4 5 6 8 9 10 12 13 14 16 To delete a single row and a single

问题 How can I delete one or more rows and/or columns from an array? 回答1: Working with: julia> array = [1 2 3 4; 5 6 7 8; 9 10 11 12; 13 14 15 16] 4×4 Array{Int64,2}: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 To delete a single row (here row 2): julia> newarray = array[1:end .!= 2, :] 3×4 Array{Int64,2}: 1 2 3 4 9 10 11 12 13 14 15 16 To delete a single column (here column 3): julia> newarray = array[:, 1:end .!= 3] 4×3 Array{Int64,2}: 1 2 4 5 6 8 9 10 12 13 14 16 To delete a single row and a single

问题 How can I delete one or more rows and/or columns from an array? 回答1: Working with: julia> array = [1 2 3 4; 5 6 7 8; 9 10 11 12; 13 14 15 16] 4×4 Array{Int64,2}: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 To delete a single row (here row 2): julia> newarray = array[1:end .!= 2, :] 3×4 Array{Int64,2}: 1 2 3 4 9 10 11 12 13 14 15 16 To delete a single column (here column 3): julia> newarray = array[:, 1:end .!= 3] 4×3 Array{Int64,2}: 1 2 4 5 6 8 9 10 12 13 14 16 To delete a single row and a single

问题 I am unable to find in the C standard docs specifically where it says that multidimensional arrays are contiguous. While it can be inferred from the fact that array elements are contiguous, I want some perspective from the community. The following code prints out the numbers in the order that I would expect, which is 1 - 9. #include <stdio.h> int main() { int a[][3] = {{1,2,3},{4,5,6},{7,8,9}}; int* p = (int*)a; int i; for (i = 0; i < sizeof(a)/sizeof(int); i++) printf("%d ",p[i]); return 0;