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使用App Inventor扩展实现多点触控：Rotation Detector · App Inventor 2 中文网
...tents
rver.
Keep in mind that the extensions mechanism is still unstable and under development. Any aia files you build in steps (1) a
Using App Inventor extensions to implement multitouch: Rotation detector
A demo app with rotation detector extension component
How to build rotation detector...
Scala: what is the best way to append an element to an Array?
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You can use :+ to append element to array and +: to prepend it:
0 +: array :+ 4
should produce:
res3: Array[Int] = Array(0, 1, 2, 3, 4)
It's the same as with any other implementation of Seq.
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How can I print a circular structure in a JSON-like format?
I have a big object I want to convert to JSON and send. However it has circular structure. I want to toss whatever circular references exist and send whatever can be stringified. How do I do that?
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What's the difference setting Embed Interop Types true and false in Visual Studio?
... Types off. The difference is mentioned here: “C# 4, and later versions, converts the returned Object to dynamic automatically if the assembly is referenced by the /link compiler option or, equivalently, if the Excel Embed Interop Types property is set to true. True is the default value for this p...
How enumerate all classes with custom class attribute?
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Of course Resharper says "that foreach loop can be converted into a LINQ expression" which looks like this: assembly.GetTypes().Where(type => type.GetCustomAttributes(typeof(HelpAttribute), true).Length > 0);
– David Barrows
Oct 1...
Choose between ExecutorService's submit and ExecutorService's execute
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There is a difference concerning exception/error handling.
A task queued with execute() that generates some Throwable will cause the UncaughtExceptionHandler for the Thread running the task to be invoked. The default UncaughtExceptionHandler, which typically prints the Thro...
Elegant method to generate array of random dates within two dates
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You can convert the boundary dates to integers (Date.getTime()) and then use Math.random() to generate your random dates within given boundaries. Then go back to Date objects with Date.setTime().
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How to open standard Google Map application from my application?
...passing label to google maps with latitude and longitude , map application converts the label into the addresses. Can you please tell that how to solve this problem?
– Rohan Sharma
Mar 9 '18 at 18:54
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Aggregate / summarize multiple variables per group (e.g. sum, mean)
...[, lapply(.SD, sum), by=.(year, month), .SDcols=c("x1","x2")]
setDF(df2) # convert back to dataframe
Using the plyr package
require(plyr)
df2 <- ddply(df1, c("year", "month"), function(x) colSums(x[c("x1", "x2")]))
Using summarize() from the Hmisc package
(column headings are messy in my ex...
Create ArrayList from array
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Yep. And in the (most common) case where you just want a list, the new ArrayList call is unecessary as well.
– Calum
Oct 1 '08 at 14:41
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