All Questions
2,211,601
questions
960
votes
25
answers
877k
views
Scanner is skipping nextLine() after using next() or nextFoo()?
I am using the Scanner methods nextInt() and nextLine() for reading input.
It looks like this:
System.out.println("Enter numerical value");
int option;
option = input.nextInt(); // Read ...
- 10.5k
162
votes
1
answer
77k
views
What to do with mysqli problems? Errors like mysqli_fetch_array(): Argument #1 must be of type mysqli_result and such
In my local/development environment, the MySQLi query is performing OK. However, when I upload it on my web host environment, I get this error:
Fatal error: Call to a member function bind_param() on ...
- 1,783
788
votes
4
answers
315k
views
SQL injection that gets around mysql_real_escape_string()
Is there an SQL injection possibility even when using mysql_real_escape_string() function?
Consider this sample situation. SQL is constructed in PHP like this:
$login = mysql_real_escape_string(...
- 82.8k
1547
votes
14
answers
1.8m
views
How to join (merge) data frames (inner, outer, left, right)
Given two data frames:
df1 = data.frame(CustomerId = c(1:6), Product = c(rep("Toaster", 3), rep("Radio", 3)))
df2 = data.frame(CustomerId = c(2, 4, 6), State = c(rep("Alabama", 2), rep("Ohio", 1)))
...
- 24.7k
629
votes
5
answers
75k
views
How can I pivot a dataframe? [closed]
What is pivot?
How do I pivot?
Long format to wide format?
I've seen a lot of questions that ask about pivot tables, even if they don't know it. It is virtually impossible to write a canonical ...
- 292k
931
votes
8
answers
438k
views
Pandas Merging 101
How can I perform a (INNER| (LEFT|RIGHT|FULL) OUTER) JOIN with pandas?
How do I add NaNs for missing rows after a merge?
How do I get rid of NaNs after merging?
Can I merge on the index?
How do I ...
- 397k
3444
votes
34
answers
273k
views
The Mutable Default Argument in Python
Anyone tinkering with Python long enough has been bitten (or torn to pieces) by the following issue:
def foo(a=[]):
a.append(5)
return a
Python novices would expect this function called with ...
- 142k
55
votes
6
answers
91k
views
I'm getting an IndentationError (or a TabError). How do I fix it?
I have a Python script:
if True:
if False:
print('foo')
print('bar')
However, when I attempt to run my script, Python raises an IndentationError:
File "script.py", line 4
...
- 22.7k
3316
votes
24
answers
2.2m
views
How do I clone a list so that it doesn't change unexpectedly after assignment?
While using new_list = my_list, any modifications to new_list changes my_list every time. Why is this, and how can I clone or copy the list to prevent it? For example:
>>> my_list = [1, 2, 3]
...
- 66.2k
885
votes
23
answers
559k
views
Unfortunately MyApp has stopped. How can I solve this?
I am developing an application, and everytime I run it, I get the message:
Unfortunately, MyApp has stopped.
What can I do to solve this?
About this question - obviously inspired by What is a ...
- 100k
207
votes
12
answers
107k
views
What do querySelectorAll() and getElementsBy*() methods return?
Do getElementsByClassName (and similar functions like getElementsByTagName and querySelectorAll) work the same as getElementById or do they return an array of elements?
The reason I ask is because I ...
- 5,211
7615
votes
86
answers
1.6m
views
How do JavaScript closures work?
How would you explain JavaScript closures to someone with a knowledge of the concepts they consist of (for example functions, variables and the like), but does not understand closures themselves?
I ...
2470
votes
10
answers
1.0m
views
What are the basic rules and idioms for operator overloading?
Note: This question and the original answers are from 2010 and partially outdated. Most of it is still good and helpful, but the original text no longer covers everything there is to know about C++ ...
- 223k
4228
votes
33
answers
3.6m
views
Is there a CSS parent selector?
How do I select the <li> element that is a direct parent of the anchor element?
As an example, my CSS would be something like this:
li < a.active {
property: value;
}
Obviously there are ...
- 57.7k
652
votes
3
answers
143k
views
What is the explicit promise construction antipattern and how do I avoid it?
I was writing code that does something that looks like:
function getStuffDone(param) {
return new Promise(function(resolve, reject) {
myPromiseFn(param+1)
.then(function(val) {
...
- 275k