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Joining two lists together
...e list a. If you wanted to preserve the original lists then you should use Concat (as pointed out in the other answers):
var newList = a.Concat(b);
This returns an IEnumerable as long as a is not null.
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How can I concatenate two arrays in Java?
I need to concatenate two String arrays in Java.
61 Answers
61
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What is the purpose of “!” and “?” at the end of method names?
... Beware, this isn't always the case. For example, Ruby Array#concat docs.ruby-lang.org/en/2.0.0/Array.html#method-i-concat. Where you can get burnt badly is something like MyActiveRecordModel.column_names.concat(...). Instead you must clone it before doing the concat.
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How to remove leading and trailing whitespace in a MySQL field?
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I downvoted. Testcase: SELECT CONCAT('"', TRIM(" hello world "), '"') AS `trimmed value` FROM DUAL gives the wanted output "hello world". While the replace variant dangerously removes the space as word separator: SELECT CONCAT('"', REPLACE(" hello world "...
LEFT JOIN only first row
...ect only the first item in a LEFT JOIN.
You can use a subquery that GROUP_CONCATS what you want (sorted, too!), then just split the GROUP_CONCAT'd result and take only its first item, like so...
LEFT JOIN Person ON Person.id = (
SELECT SUBSTRING_INDEX(
GROUP_CONCAT(FirstName ORDER BY F...
How to append something to an array?
...ant to add the items of one array to another array, you can use firstArray.concat(secondArray):
var arr = [
"apple",
"banana",
"cherry"
];
arr = arr.concat([
"dragonfruit",
"elderberry",
"fig"
]);
console.log(arr);
Update
Just an addition to this answer if you want to prepend...
Why is it Valid to Concatenate Null Strings but not to Call “null.ToString()”?
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The reason for first one working:
From MSDN:
In string concatenation operations,the C# compiler treats a null string the same as an empty string, but it does not convert the value of the original null string.
More information on the + binary operator:
The binary + operator perf...
Iterate two Lists or Arrays with one ForEach statement in C#
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You can use Union or Concat, the former removes duplicates, the later doesn't
foreach (var item in List1.Union(List1))
{
//TODO: Real code goes here
}
foreach (var item in List1.Concat(List1))
{
//TODO: Real code goes here
}
...
Is there a performance gain in using single quotes vs double quotes in ruby?
... x.report("assign double") { n.times do; c = "a string"; end}
x.report("concat single") { n.times do; 'a string ' + 'b string'; end}
x.report("concat double") { n.times do; "a string " + "b string"; end}
end
$ ruby benchmark_quotes.rb
user system total r...
Import multiple csv files into pandas and concatenate into one DataFrame
I would like to read several csv files from a directory into pandas and concatenate them into one big DataFrame. I have not been able to figure it out though. Here is what I have so far:
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