How do I reverse an int array in Java?
To reverse an int array, you swap items up until you reach the midpoint, like this: The way you are doing it, you swap each element twice, so the result is the same as the initial list.
arrays
“Expected expression before ‘ { ‘ token”
Best to do the init’ing at declaration time: Only the arrays need to be done that way, but it’s best to do them all the same way. Your alternative is
Convert pandas dataframe to NumPy array
df.to_numpy() is better than df.values, here’s why.* It’s time to deprecate your usage of values and as_matrix(). pandas v0.24.0 introduced two new methods for obtaining NumPy arrays from pandas objects: to_numpy(), which is defined on Index, Series, and DataFrame objects, and array, which is defined on Index and Series objects only. If you visit the v0.24 docs for .values, you will see a big red warning that says: Warning: We recommend … Read more
What is the way of declaring an array in JavaScript?
The preferred way is to always use the literal syntax with square brackets; its behaviour is predictable for any number of items, unlike Array‘s. What’s more, Array is not a keyword, and although it is not a realistic situation, someone could easily overwrite it: However, the larger issue is that of consistency. Someone refactoring code could come across … Read more
What is the difference between String[] and String… in Java?
How should I declare main() method in Java? String[] and String… are the same thing internally, i. e., an array of Strings. The difference is that when you use a varargs parameter (String…) you can call the method like: And when you declare the parameter as a String array you MUST call this way: What’s actually the difference between String[] and String… if … Read more
“Notice: Undefined variable”, “Notice: Undefined index”, and “Notice: Undefined offset” using PHP
Notice: Undefined variable From the vast wisdom of the PHP Manual: Relying on the default value of an uninitialized variable is problematic in the case of including one file into another which uses the same variable name. It is also a major security risk with register_globals turned on. E_NOTICE level error is issued in case of working with uninitialized variables, however not … Read more
How do I declare a 2d array in C++ using new?
If your row length is a compile time constant, C++11 allows See this answer. Compilers like gcc that allow variable-length arrays as an extension to C++ can use new as shown here to get fully runtime-variable array dimension functionality like C99 allows, but portable ISO C++ is limited to only the first dimension being variable. Another efficient option is … Read more
Adding values to a C# array
You can do this way – Alternatively, you can use Lists – the advantage with lists being, you don’t need to know the array size when instantiating the list. Edit: a) for loops on List<T> are a bit more than 2 times cheaper than foreach loops on List<T>, b) Looping on array is around 2 times cheaper than looping on … Read more
All possible array initialization syntaxes
These are the current declaration and initialization methods for a simple array. Note that other techniques of obtaining arrays exist, such as the Linq ToArray() extensions on IEnumerable<T>. Also note that in the declarations above, the first two could replace the string[] on the left with var (C# 3+), as the information on the right is enough to infer the proper type. … Read more
How can I reverse an array in JavaScript without using libraries?
Javascript has a reverse() method that you can call in an array Not sure if that’s what you mean by ‘libraries you can’t use’, I’m guessing something to do with practice. If that’s the case, you can implement your own version of .reverse() Do note that the built-in .reverse() method operates on the original array, thus you don’t need to … Read more