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How do you calculate log base 2 in Java for integers?
...oid FP calculations whenever possible.
Floating-point operations are not exact. You can never know for sure what will (int)(Math.log(65536)/Math.log(2)) evaluate to. For example, Math.ceil(Math.log(1<<29) / Math.log(2)) is 30 on my PC where mathematically it should be exactly 29. I didn't fi...
Way to go from recursion to iteration
... on the outside, you just pop an action/continuation off the stack, apply/execute it, push the actions it returned on the stack in reverse in order and repeat. Contingent/complex traversals, you just capture what would have been local stack variables in reference-counted pointers that you close ov...
Java 8: Lambda-Streams, Filter by Method with Exception
I have a problem trying out the Lambda expressions of Java 8.
Usually it works fine, but now I have methods that throw IOException 's.
It's best if you look at the following code:
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Linq code to select one item
...
Depends how much you like the linq query syntax, you can use the extension methods directly like:
var item = Items.First(i => i.Id == 123);
And if you don't want to throw an error if the list is empty, use FirstOrDefault which returns the default value for the elem...
Can't find the PostgreSQL client library (libpq)
I'm trying to install PostgreSQL for Rails on Mac OS X 10.6. First I tried the MacPorts install but that didn't go well so I did the one-click DMG install. That seemed to work.
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Pandas conditional creation of a series/dataframe column
...elect from:
df['color'] = np.where(df['Set']=='Z', 'green', 'red')
For example,
import pandas as pd
import numpy as np
df = pd.DataFrame({'Type':list('ABBC'), 'Set':list('ZZXY')})
df['color'] = np.where(df['Set']=='Z', 'green', 'red')
print(df)
yields
Set Type color
0 Z A green
1 ...
python: how to identify if a variable is an array or a scalar
...ad of list.
note: isinstance also supports a tuple of classes, check type(x) in (..., ...) should be avoided and is unnecessary.
You may also wanna check not isinstance(x, (str, unicode))
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What are free monads?
... some time, but everyone just seems to use/discuss them without giving an explanation of what they are. So: what are free monads? (I'd say I'm familiar with monads and the Haskell basics, but have only a very rough knowledge of category theory.)
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Relative frequencies / proportions with dplyr
...nt to calculate the proportion of different values within each group. For example, using the mtcars data, how do I calculate the relative frequency of number of gears by am (automatic/manual) in one go with dplyr ?
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How do you make an array of structs in C?
...nt month;
int year;
}STUDENT;
int numStudents=3;
int x;
STUDENT* students = malloc(numStudents * sizeof *students);
for (x = 0; x < numStudents; x++){
students[x].firstName=(char*)malloc(sizeof(char*));
scanf("%s",students[x].firstName);
stude...