indexing

问题 Given an array d = np.random.randn(100) and an index array i = np.random.random_integers(low=3, high=d.size - 5, size=20) how can I efficiently create a 2d array r with r.shape = (20, 8) such that for all j=0..19 , r[j] = d[i[j]-3:i[j]+5] In my case, the arrays are quite large (~200000 instead of 100 and 20), so something quick would be useful. 回答1: You can create a windowed view of your data, i.e. a (93, 8) array, where item [i, j] is item [i+j] of your original array, as: >>> from numpy.lib

问题 We are planning to create an table like below in production environment but concerning about what would happen to storage and query/insert/update performance if we create a constraint key with quite a lot of fields in MySQL like this: create table table_name ( f1 int null, f2 int null, f3 int null, f4 int null, f5 int null, f6 int null, f7 int null, f8 int null, f9 int null, f10 int null, f11 int null, f12 int null, f13 int null, f14 int null, f15 int null, f16 int null, f17 int null, f18 int

问题 I need to remove the last occurrence of a specific element in a [Bool] Array. For example in JavaScript this would be: var k = [true, true, false]; k.splice(k.lastIndexOf(true), 1); ==> [true, false] How would I achieve the same behavior in Swift? 回答1: You can easily find the last occurrence of a value by enumerating in reverse. When you find the value you're looking for, just remove it and break from the loop. Use reverse() enumerate the range of indexes in reverse order: for i in array

问题 I'm trying to define a property that is not the id as a clustered index in nhibernate, yet I've found no way of doing this. Could anyone give me a pointer of how this is done, or it is something not currently available in nhibernate? Thanks in advance 回答1: You can use <database-object> to create indexes and other artifacts. http://nhibernate.info/doc/nhibernate-reference/mapping.html#mapping-database-object 来源： https://stackoverflow.com/questions/3070355/setting-clustered-index-in-nhibernate

问题 I have read about how boolean columns don't serve much as searching indexes.. But my question is.. if a clustered index, affects the physical arrangement of the records can't it be used to put a type of records, all together (in the same page) so that those page will have less chance of being loaded into memory.. I will try to explain better: for the table [BookPages] ID(int) Deleted(Boolean) Text(Varchar) if the clustered index is on ID column, a sample data would be 1, true, 'the quick..' 2

问题 I am very new to C and I am hoping for some pointers. I am attempting to take an input of 7 integers of an array and search through them to see if any number appears only once. Here is what I have so far: #define size 7 int main(void) { int array[size], target, i, prev, count; //Initialize the array printf("Please enter %d integers", size); scanf("%d", &target); prev = array[0]; count = 1; for(i = 0; i<size; i++) { scanf("%d", &array[i]); ... I realize it is quite terrible but C is completely

问题 Does a SQL Server Computed Column require "persistence" in order for it to be indexed efficiently? It's a Name and a LoweredName (computed) column combination. So I don't believe it deals with the precision stuff mentioned in a MSDN article. 回答1: Contrary to what Mitch has stated, you don't need a column to be persisted for an index to be created (what the MSDN article states is that, if the computed column is not deterministic , then it has to be marked persisted before it can be considered

问题 I just wanted to know how it is possible to to update (delete/insert) a document based on a numeric field. So far I did this: LuceneManager.updateDocument(writer, new Term("id", NumericUtils.intToPrefixCoded(sentenceId)), newDoc); But now with Lucene 4.0 the NumericUtils class has changed to this which I don't really understand. Any help? 回答1: I would recommend, if possible, it would be better to store an ID as a keyword string, rather than a number. If it is simply a unique identifier,

问题 I have a table in my DB (Postgres 9.3.4) with index on couple of columns. Also I have a view based only on this table with grouping and filter by indexed columns. CREATE OR REPLACE VIEW vstatement_base AS SELECT o.bitrnrequestid AS bitrnreqid, o.icardid, o.icardaccountid, o.iterminalid, abs(sum( CASE WHEN o.sitypeex = ANY (ARRAY[1, 11]) THEN o.namount ELSE 0::numeric END)) AS charged, abs(sum( CASE WHEN o.sitypeex = ANY (ARRAY[2, 12]) THEN o.namount ELSE 0::numeric END)) AS withdrawn FROM

问题 In oracle if you had a table with say 3 indexes on 3 different columns. How many of those indexes could a single SQL statement possibly use from the one table? 回答1: It's possible that all three could be used. It's not particularly likely that Oracle would use all three, or that using all three would be beneficial, but it's possible. The simplest way for Oracle to use all three indexes would be if we were talking about bitmap indexes, which are designed to be combined, but are really only