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What is the difference between persist() and merge() in JPA and Hibernate?
...avadoc:
The semantics of the persist
operation, applied to an entity X are
as follows:
If X is a new entity, it
becomes managed. The entity X will be
entered into the database at or before
transaction commit or as a result of
the flush operation.
If X is a
preexisting ma...
How to append rows to an R data frame
...ined as:
# pre-allocate space
f3 <- function(n){
df <- data.frame(x = numeric(n), y = character(n), stringsAsFactors = FALSE)
for(i in 1:n){
df$x[i] <- i
df$y[i] <- toString(i)
}
df
}
Here's a similar approach, but one where the data.frame is created as the last step.
...
WPF ListView turn off selection
...gt;
<ListView.ItemContainerStyle>
<Style TargetType="{x:Type ListViewItem}">
<Style.Triggers>
<Trigger Property="IsSelected"
Value="True">
<Setter Property="Background"
...
Behaviour of increment and decrement operators in Python
...d - unary operators only work on numbers, but I presume that you wouldn't expect a hypothetical ++ operator to work on strings.)
++count
Parses as
+(+count)
Which translates to
count
You have to use the slightly longer += operator to do what you want to do:
count += 1
I suspect the ++ an...
How to find the size of localStorage
...
Execute this snippet in JavaScript console (one line version):
var _lsTotal=0,_xLen,_x;for(_x in localStorage){ if(!localStorage.hasOwnProperty(_x)){continue;} _xLen= ((localStorage[_x].length + _x.length)* 2);_lsTotal+=_xLen;...
What's a concise way to check that environment variables are set in a Unix shell script?
I've got a few Unix shell scripts where I need to check that certain environment variables are set before I start doing stuff, so I do this sort of thing:
...
What is an idempotent operation?
...effect if it is called more than once with the same input parameters. For example, removing an item from a set can be considered an idempotent operation on the set.
In mathematics, an idempotent operation is one where f(f(x)) = f(x). For example, the abs() function is idempotent because abs(abs(x))...
Breaking out of nested loops [duplicate]
Is there an easier way to break out of nested loops than throwing an exception? (In Perl, you can give labels to each loop and at least continue an outer loop.)
...
Header files for x86 SIMD intrinsics
Which header files provide the intrinsics for the different x86 SIMD instruction set extensions (MMX, SSE, AVX, ...)? It seems impossible to find such a list online. Correct me if I'm wrong.
...
How to compare type of an object in Python?
...use basestr, not str. otherwise you will not pick unicode. (although for 3.x I think str is the basestr)
– hasen
Apr 3 '09 at 0:45
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