indexing

问题 I have a query making an addition of several column values in the WHERE clause. I can't precompute this addition in a single column because the combination of columns to use varies between queries. My problem is that my table is very large (several hundreds of millions of rows) and the performances very bad. Example table: +---------+------------+--------+--------+--------+--------+ | tableId | categoryId | value1 | value2 | value3 | value4 | +---------+------------+--------+--------+--------

问题 I'm trying to process a fairly large dataset that doesn't fit into memory using Pandas when loading it at once so I'm using Dask. However, I'm having difficulty in adding a unique ID column to the dataset once read when using the read_csv method. I keep getting an error (see Code). I'm trying to create an index column so I can set that new column as the index for the data, but the error appears to be telling me to set the index first before creating the column. CODE df = dd.read_csv(r'path\to

问题 This question already has answers here : Dynamically filtering a pandas dataframe (3 answers) Closed 2 years ago . I am trying to select individual rows from a multiindex dataframe using a list of multiindices. For example. I have got the following dataframe: Col1 A B C 1 1 1 -0.148593 2 2.043589 2 3 -1.696572 4 -0.249049 2 1 5 2.012294 6 -1.756410 2 7 0.476035 8 -0.531612 I would like to select all 'C' with (A,B) = [(1,1), (2,2)] Col1 A B C 1 1 1 -0.148593 2 2.043589 2 2 7 0.476035 8 -0

问题 I encounter error in index and match functions when the counter of date changes. I wrote a comment when I face with error. I uploaded a sample of my data if it needed. sample : http://s000.tinyupload.com/?file_id=00243748825638974221 here is the code : Sub regionalAverage() Application.ScreenUpdating = False Application.DisplayStatusBar = False Application.EnableEvents = False ActiveSheet.DisplayPageBreaks = False ' *** change the declaration here *** Dim aname() As String Dim rw As Variant

问题 How to increase select statement speed in Postgres 9.0 ? Table has required index present. Desired result can obtained using index (kuupaev,kellaaeg) immediately. However Postgres scans all rows: explain analyze SELECT max( kuupaev||kellaaeg ) as res from firma2.ALGSA where laonr=1 and kuupaev <=current_date and (kuupaev,kellaaeg) <= ( current_date, '23 59' ) "Aggregate (cost=6932.65..6932.67 rows=1 width=10) (actual time=1608.590..1608.592 rows=1 loops=1)" " -> Seq Scan on algsa (cost=0.00.

问题 I'm very new to Solr. I succeeded in indexing data from my sql database via DIH. Now I want to import xml files and index them also via DIH but it just won't work! My data-config.xml looks like this: <dataConfig> <dataSource type="FileDataSource" encoding="UTF-8" /> <document> <entity name="dir" processor="FileListEntityProcessor" baseDir="/bla/test2" fileName=".*xml" stream="true" recursive="false" rootEntity="false"> <entity name="PubmedArticle" processor="XPathEntityProcessor" transformer=

问题 Say I have a matrix A, and I want to construct a matrix B that contains all rows of B that start with a particular number. How? Thanks 回答1: Select all rows of B into A, where the first colum of B has value n: A = B(B(:,1) == n,:); In contrast to that, the following selects all rows of B into A, starting from row index n: A = B(n:end,:); 来源： https://stackoverflow.com/questions/5561007/matlab-select-all-rows-starting-with-a-particular-number

问题 Say I have a matrix A, and I want to construct a matrix B that contains all rows of B that start with a particular number. How? Thanks 回答1: Select all rows of B into A, where the first colum of B has value n: A = B(B(:,1) == n,:); In contrast to that, the following selects all rows of B into A, starting from row index n: A = B(n:end,:); 来源： https://stackoverflow.com/questions/5561007/matlab-select-all-rows-starting-with-a-particular-number

问题 I've been trying to work this out: Say I have an array: int[] n = {0, 0, -1, 1, 0, 1, 1, -1, 1}; I need to be able to sort through the array and if there is a zero with a non zero preceding it, then they should be swapped. For example: 0, 0, -1, 1, 0, 1, 1, -1, 1 will become: 0, 0, -1, 0, 1, 1, 1, -1, 1 I have been trying to do it using a for loop and if statements with no luck. Any tips? 回答1: Try this: for (int i = 1 ; i < n.length ; i++) if (n[i] == 0 && n[i - 1] != 0) { int tmp = n[i - 1];

问题 I've been trying to work this out: Say I have an array: int[] n = {0, 0, -1, 1, 0, 1, 1, -1, 1}; I need to be able to sort through the array and if there is a zero with a non zero preceding it, then they should be swapped. For example: 0, 0, -1, 1, 0, 1, 1, -1, 1 will become: 0, 0, -1, 0, 1, 1, 1, -1, 1 I have been trying to do it using a for loop and if statements with no luck. Any tips? 回答1: Try this: for (int i = 1 ; i < n.length ; i++) if (n[i] == 0 && n[i - 1] != 0) { int tmp = n[i - 1];