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Summarizing multiple columns with dplyr? [duplicate]
... 2.87
#> 3 3 2.85 2.95 2.95 3.06
Also don't forget about data.table (use keyby to sort sort groups):
library(data.table)
setDT(df)[, lapply(.SD, mean), keyby = grp]
#> grp a b c d
#> 1: 1 3.079412 2.979412 2.979412 2.914706
#> 2: 2 3.029126 3....
Use didSelectRowAtIndexPath or prepareForSegue method for UITableView?
I'm using storyboards and I have a UITableView. I have a segue setup that pushes from my table to the detail VC. But which method should I use to handle this? I'll have to pass a couple objects to the detail view. But do I use didSelectRowAtIndex or -(void)prepareForSegue:(UIStoryboardSegue *...
Cannot insert explicit value for identity column in table 'table' when IDENTITY_INSERT is set to OFF
...tionId that is an identity column.
You can turn on identity insert on the table like this so that you can specify your own identity values.
SET IDENTITY_INSERT Table1 ON
INSERT INTO Table1
/*Note the column list is REQUIRED here, not optional*/
(OperationID,
OpDescription...
What are the applications of binary trees?
...nary Tries - Used in almost every high-bandwidth router for storing router-tables.
Hash Trees - used in p2p programs and specialized image-signatures in which a hash needs to be verified, but the whole file is not available.
Heaps - Used in implementing efficient priority-queues, which in turn are u...
How can I insert values into a table, using a subquery with more than one result?
...
If you are inserting one record into your table, you can do
INSERT INTO yourTable
VALUES(value1, value2)
But since you want to insert more than one record, you can use a SELECT FROM in your SQL statement.
so you will want to do this:
INSERT INTO prices (group,...
Why does MYSQL higher LIMIT offset slow the query down?
Scenario in short: A table with more than 16 million records [2GB in size]. The higher LIMIT offset with SELECT, the slower the query becomes, when using ORDER BY *primary_key*
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Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_
...itectural register operands onto physical registers. Presumably it needs a table of uop-code -> dependency pattern and port choices, and grouping all uops for the same execution unit together simplifies that table. That's what I meant in more detail.
– Peter Cordes
...
Practical usage of setjmp and longjmp in C
...r to free the memory. Also, this does not have so many blasted exceptions tables that all C++ compilers still generate 20 years after the fact.
– artless noise
Mar 10 '13 at 2:51
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How to remove not null constraint in sql server using query
...
ALTER TABLE YourTable ALTER COLUMN YourColumn columnType NULL
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Wrap a delegate in an IEqualityComparer
...ll of these rely on hash codes to work properly, because they utilize hash tables internally for efficiency.
Take Distinct, for example. Consider the implications of this extension method if all it utilized were an Equals method. How do you determine whether an item's already been scanned in a sequ...