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How can I determine if a variable is 'undefined' or 'null'?
...enceError and break execution if variable is not defined or referred to at all in the code, using typeof is safer.
– Mani Gandham
Jun 15 '14 at 9:49
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Summarizing multiple columns with dplyr? [duplicate]
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The dplyr package contains summarise_all for this aim:
library(dplyr)
df %>% group_by(grp) %>% summarise_all(list(mean))
#> # A tibble: 3 x 5
#> grp a b c d
#> <int> <dbl> <dbl> <dbl> <dbl>
#>...
How do I completely uninstall Node.js, and reinstall from beginning (Mac OS X)
My version of node is always v0.6.1-pre even after I install brew node and NVM install v0.6.19.
28 Answers
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How to get JQuery.trigger('click'); to initiate a mouse click
... if one of the hrefs on the <a tag is '#', that would do it. <a normally redirects to a different URL. You must stop it with ev.preventDefault() and ev.stopPropagation() before your click handler returns. OR, use some other tag besides <a; you can attach click handlers to anything that's...
How do I add indices to MySQL tables?
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ALTER TABLE `table` ADD INDEX `product_id_index` (`product_id`)
Never compare integer to strings in MySQL. If id is int, remove the quotes.
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How to copy a selection to the OS X clipboard
...xists only for X11 (unless you build vim with +X11 support, which will install a X11 server XQuartz in OS X), while OS X doesn't use X11 as its windows system.
– nn0p
Nov 27 '16 at 18:20
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adding multiple entries to a HashMap at once in one statement
... 2016) as follow:
Map<String, Integer> cities = Map.of("Brussels", 1_139000, "Cardiff", 341_000);
The var-args case for Map is a little bit harder, you need to have both keys and values, but in Java, methods can’t have two var-args parameters. So the general case is handled by taking a va...
Is there some way to PUSH data from web server to browser?
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Yes, what you're looking for is COMET http://en.wikipedia.org/wiki/Comet_(programming). Other good Google terms to search for are AJAX-push and reverse-ajax.
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android asynctask sending callbacks to ui [duplicate]
...tivity I'm initializing the asynctask, and I want the asynctask to report callbacks back to my activity.
Is it possible? Or does the asynctask must be in the same class file as the activity?
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How many threads can a Java VM support?
...ts.
There are several parameters here. The specific VM, plus there are usually run-time parameters on the VM as well. That's somewhat driven by the operating system: what support does the underlying OS have for threads and what limitations does it put on them? If the VM actually uses OS-level thr...