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How to change a nullable column to not nullable in a Rails migration?
...s:
# Make sure no null value exist
MyModel.where(date_column: nil).update_all(date_column: Time.now)
# Change the column to not allow null
change_column :my_models, :date_column, :datetime, null: false
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Knight's Shortest Path on Chessboard
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You have a graph here, where all available moves are connected (value=1), and unavailable moves are disconnected (value=0), the sparse matrix would be like:
(a1,b3)=1,
(a1,c2)=1,
.....
And the shortest path of two points in a graph can be found usin...
How are feature_importances in RandomForestClassifier determined?
...d in [1] (often cited, but unfortunately rarely read...). It is sometimes called "gini importance" or "mean decrease impurity" and is defined as the total decrease in node impurity (weighted by the probability of reaching that node (which is approximated by the proportion of samples reaching that no...
How to add Google Analytics Tracking ID to GitHub Pages
... I have added them, however Google analytics say the Tracking is not installed. My page as specified in G-Analytics is http://avi-aryan.github.io
– Avi
Jul 15 '13 at 12:33
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Avoid trailing zeroes in printf()
...ing your number is in the variable num, the following function will remove all but the first N decimals, then strip off the trailing zeros (and decimal point if they were all zeros).
char str[50];
sprintf (str,"%.20g",num); // Make the number.
morphNumericString (str, 3);
: :
void morphNumericS...
How to grep Git commit diffs or contents for a certain word?
In a Git code repository I want to list all commits that contain a certain word. I tried this
8 Answers
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How to split text without spaces into list of words?
...el the distribution of the output. A good first approximation is to assume all words are independently distributed. Then you only need to know the relative frequency of all words. It is reasonable to assume that they follow Zipf's law, that is the word with rank n in the list of words has probabilit...
How to extract a git subdirectory and make a submodule out of it?
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Nowadays there's a much easier way to do it than manually using git filter-branch: git subtree
Installation
NOTE git-subtree is now part of git (if you install contrib) as of 1.7.11, so you might already have it installed. You may check by executing git subtree.
To install...
Example for boost shared_mutex (multiple reads/one write)?
I have a multithreaded app that has to read some data often, and occasionally that data is updated. Right now a mutex keeps access to that data safe, but it's expensive because I would like multiple threads to be able to read simultaneously, and only lock them out when an update is needed (the updat...
Seeking clarification on apparent contradictions regarding weakly typed languages
...xamples of programming languages that simply coerce/convert types automatically.
9 Answers
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