indexing

问题 I have a problem filtering a pandas dataframe. city NYC NYC NYC NYC SYD SYD SEL SEL ... df.city.value_counts() I would like to remove rows of cities that has less than 4 count frequency , which would be SYD and SEL for instance. What would be the way to do so without manually dropping them city by city? 回答1: Here you go with filter df.groupby('city').filter(lambda x : len(x)>3) Out[1743]: city 0 NYC 1 NYC 2 NYC 3 NYC Solution two transform sub_df = df[df.groupby('city').city.transform('count'

问题 There seem to be a number of ways to handle a multiple foreign key association. Each way I have approached this has their draw backs, and as I am new to Rails I am convinced others have come across a similar scenario and I am probably working on something solved long ago. My question is: What would be an efficient way of handling a multiple index key association, while still retaining all other Rails sql modifiers (such as :include etc)? My scenario is: I have a table association as follows

问题 So now that Indexes are available in latest beta version of Entity Framework 6.1 is it even possible to create an index in code first approach that is equal to this SQL statement? CREATE NONCLUSTERED INDEX [Sample1] ON [dbo].[Logs] ([SampleId],[Date]) INCLUDE ([Value]) 回答1: Strictly speaking it has been always possible in Code First Migrations because you can run sql in a migration: public partial class AddIndexes : DbMigration { private const string IndexName = "IX_LogSamples"; public

问题 Lucene is an excellent search engine, but the .NET version is behind the official Java release (latest stable .NET release is 2.0, but the latest Java Lucene version is 2.4, which has more features). How do you get around this? 回答1: One way I found, which was surprised could work: Create a .NET DLL from a Java .jar file! Using IKVM you can download Lucene, get the .jar file, and run: ikvmc -target:library <path-to-lucene.jar> which generates a .NET dll like this: lucene-core-2.4.0.dll You can

问题 I've accidentally added a new filter to my GAE application. The status of the index is 'serving' now - however I don't need that index at all and I'd like to remove. How can I do that? 回答1: It is documented here. Hope that helps. Deleting Unused Indexes When you change or remove an index from index.yaml, the original index is not deleted from App Engine automatically. This gives you the opportunity to leave an older version of the app running while new indexes are being built, or to revert to

问题 I've accidentally added a new filter to my GAE application. The status of the index is 'serving' now - however I don't need that index at all and I'd like to remove. How can I do that? 回答1: It is documented here. Hope that helps. Deleting Unused Indexes When you change or remove an index from index.yaml, the original index is not deleted from App Engine automatically. This gives you the opportunity to leave an older version of the app running while new indexes are being built, or to revert to

问题 In ActiveRecord there are two ways to declare indexes for multiple columns: add_index :classifications, [:species, :family, :trivial_names] add_index :classifications, :species add_index :classifications, :family add_index :classifications, :trivial_names Is there any difference between the first approach and the second one? If so, when should I use the first and when the second? 回答1: You are comparing a composite index with a set of independent indices. They are just different. Think of it

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 3 years ago . I'm looking for a good open source (with LGPL or a permissive license) indexing engine for a node.js application, something like Lucene. I'm looking for in-process indexing and search and am not interested in indexing servers like Sphinx or Solr. I am not afraid to create bindings for a C/C++ library either so I

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 3 years ago . I'm looking for a good open source (with LGPL or a permissive license) indexing engine for a node.js application, something like Lucene. I'm looking for in-process indexing and search and am not interested in indexing servers like Sphinx or Solr. I am not afraid to create bindings for a C/C++ library either so I

问题 This question already has answers here : Closed 6 years ago . Possible Duplicate: Why use iterators instead of array indices? I'm reviewing my knowledge on C++ and I've stumbled upon iterators. One thing I want to know is what makes them so special and I want to know why this: using namespace std; vector<int> myIntVector; vector<int>::iterator myIntVectorIterator; // Add some elements to myIntVector myIntVector.push_back(1); myIntVector.push_back(4); myIntVector.push_back(8); for