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What does the “@” symbol mean in reference to lists in Haskell?
...: ps
the list's head : p
the list's tail: pt
Without the @, you'd have to choose between (1) or (2):(3).
This syntax actually works for any constructor; if you have data Tree a = Tree a [Tree a], then t@(Tree _ kids) gives you access to both the tree and its children.
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Group query results by month and year in postgresql
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select to_char(date,'Mon') as mon,
extract(year from date) as yyyy,
sum("Sales") as "Sales"
from yourtable
group by 1,2
At the request of Radu, I will explain that query:
to_char(date,'Mon') as mon, : converts the "...
Bootstrap: Position of dropdown menu relative to navbar item
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This is the effect that we're trying to achieve:
The classes that need to be applied changed with the release of Bootstrap 3.1.0 and again with the release of Bootstrap 4. If one of the below solutions doesn't seem to be working double check the version numbe...
File changed listener in Java
I'd like to be notified when a file has been changed in the file system. I have found nothing but a thread that polls the lastModified File property and clearly this solution is not optimal.
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How to check whether a string is Base64 encoded or not
I want to decode a Base64 encoded string, then store it in my database. If the input is not Base64 encoded, I need to throw an error.
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How to search for a string in text files?
I want to check if a string is in a text file. If it is, do X. If it's not, do Y. However, this code always returns True for some reason. Can anyone see what is wrong?
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nginx upload client_max_body_size issue
I'm running nginx/ruby-on-rails and I have a simple multipart form to upload files.
Everything works fine until I decide to restrict the maximum size of files I want uploaded.
To do that, I set the nginx client_max_body_size to 1m (1MB) and expect a HTTP 413 (Request Entity Too Large) status in...
What does LayoutInflater in Android do?
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When you use a custom view in a ListView you must define the row layout.
You create an xml where you place android widgets and then in the adapter's code you have to do something like this:
public MyAdapter(Context context, List<MyObject&g...
Find all records which have a count of an association greater than zero
I'm trying to do something that I thought it would be simple but it seems not to be.
10 Answers
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How do I get the number of elements in a list?
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How to get the size of a list?
To find the size of a list, use the builtin function, len:
items = []
items.append("apple")
items.append("orange")
items.append("banana")
And now:
len(items)
returns 3.
Explanation
Everyth...