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Summarizing multiple columns with dplyr? [duplicate]
...le(1:5, 10, replace=T),
grp = sample(1:3, 10, replace=T))
# Convert to tidy format using gather
df %>%
gather(key = variable, value = value, a:d) %>%
group_by(grp, variable) %>%
summarize(mean = mean(value)) %>%
spread(variable, mean)
#> Source: local da...
When should I use Struct vs. OpenStruct?
... = 2;
Here are some common use cases.
OpenStructs can be used to easily convert hashes to one-off objects which respond to all the hash keys.
h = { a: 1, b: 2 }
o = OpenStruct.new(h)
o.a = 1
o.b = 2
Structs can be useful for shorthand class definitions.
class MyClass < Struct.new(:a,:b,:c)...
Objective-C formatting string for boolean?
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One way to do it is to convert to strings (since there are only two possibilities, it isn't hard):
NSLog(@" %s", BOOL_VAL ? "true" : "false");
I don't think there is a format specifier for boolean values.
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how to File.listFiles in alphabetical order?
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-1 I really don't understand the advantage of converting the file array to a string array and then sorting rather than just sorting the file array as the accepted answer does.
– zelanix
Feb 17 '14 at 21:49
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How to add a new row to an empty numpy array
...it would be much faster to append to a list as in your first example, then convert to a numpy array at the end, since you're really not using numpy as intended during the loop:
In [210]: %%timeit
.....: l = []
.....: for i in xrange(1000):
.....: l.append([3*i+1,3*i+2,3*i+3])
.....:...
This Handler class should be static or leaks might occur: IncomingHandler
...the whole point. Unless he has some ultra cool compiler that automatically converts inner classes to static classes when they don't use class variables.
– Sogger
Jan 7 '15 at 18:22
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What's invokedynamic and how do I use it?
...ions on the types of values supplied to its operations (e.g. Java)
Weak - converts (casts) arguments of an operation if those arguments have incompatible types (e.g. Visual Basic)
Knowing that Java is a Statically and Weakly typed, how do you implement Dynamically and Strongly typed languages on t...
Is there anything like inotify on Windows?
With the Linux OS, there is the ionotify subsystem which notifies an application of changes to the filesystem.
8 Answers
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How to output something in PowerShell
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Objects also don't get blindly converted to string, but pass through a formatter which decides on what to do with them. That's why you see Get-ChildItem's output coming in a table form, for example, and results with many properties (e.g. WMI) default to Fo...
Why doesn't the example compile, aka how does (co-, contra-, and in-) variance work?
...?
slot.get will then throw an error at runtime as it was unsuccessful in converting an Animal to Dog (duh!).
In general mutability doesn't go well with co-variance and contra-variance. That is the reason why all Java collections are invariant.
...