DolphinDB is a high performance time series database. It is written in C++ and optimized for fast injection, storage, retrieval and analysis of time series data in fields such as quantitative finance, Internet of Things, real-time analytics, etc. DolphinDB runs extremely fast. It is also easy to use as the syntax of the programming language of DolphinDB is similar to SQL and Python.
Questions tagged [dolphindb]
764 questions
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Skipping every other element in a DolphinDB array
I am trying to get an array containing every other element in my original array a. In python, I can do this with a[::2]. I wonder in what way I can do this simply and fast in DolphinDB.
I can write a for loop and repeatedly append! the every other…
Clyx
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Does DolphinDB have clause equivalent to LIMIT clause?
Usually (in MySQL) I use query like "select * from table limit 100" to peek the table, but I found it's not supported in DolphinDB. So is there any work around?
Ju Piece
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How to add a column to in-memory table in DolphinDB?
An in-memory table in DolphinDB:
t=table(10:0,`time`sym`bid`ofr,[TIMESTAMP,SYMBOL,DOUBLE,DOUBLE])
Would like to add a new column count to t, I have tried the function addColumn, it did not work.
addColumn(t,`count,[INT])
execution was completed…
Summer.H
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How to remove a composite partition in DolphinDB
To remote a composite partition in DolphinDB database, do I have to manually delete all first-level partition? Is there a command to do it in one line of code?
Bob
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how to select a row from a table for every ten rows in DolphinDB
I want to get a row per ten rows,for a example,I define a table as below,
t=table(1..1000 as id, rand(1.0, 1000) as value)
Then I want to get the rows where id%10 is 1. How to write this sql statement?
Wale
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How to delete mvccTable on disk in DolphinDB?
I created a mvccTable in DolphinDB and saved it to disk.But when I tried to delete the table folder and table files,it failed because the log.bin is "open" and in use by dolphindb.exe. How can I delete the table folder without shutting douwn the…
Summer.H
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How to modify values in a column of a DolphinDB table
I need to modify some values in a column of a DolphinDB table. But I got some error messages when executing my code.
For example, I'd like to set the 6th value to -1 in a column named id. This is my code:
t = table(1..10 as id)
t[`id][5] = -1
After…
Clyx
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Is there any command or function to monitor memory use in dolphindb?
When many users use dolphindb at the same time, I want to know the memory use of every user? Is there any function or command?
psui
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How to compute the intersection of two vectors in dolphindb?
For example, I have two vectors in dolphindb, va = [1,2,3]; vb = [2,3,5]; How can I find the intersection of va and vb?
[2,3]
psui
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How to calculate stock returns for each firm in DolphinDB
I have a table defined as bellow:
sym ="C""MS""MS""MS""IBM""IBM""C""C""C"$symbol;
price= 49.6 29.46 29.52 30.02 174.97 175.23 50.76 50.32 51.29;
qty = 2200 1900 2100 3200 6800 5400 1300 2500 8800;
timestamp =…
Wale
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Is there any easy way to determine two Table Objects Equivalent in DolphinDB
I used a method like this :
def compareTables(tb1,tb2){
if(tb1.rows() != tb2.rows()) return false
if(tb1.cols() != tb2.cols()) return false
for(colname in tb1.columnNames()){
for(row in 0:tb1.rows()){
…
HIPO.L
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Is single quotes (‘) and double quotes (") the same In DolphinDB
I execute the following code in GUI,
bigarray(symbol,0,10000000).append!(take('a',100000))
The result is displayed as bellow,
2019-03-14T14:43:23.375: execution was completed with exception
Failed to append data
Then I change the single quotes to…
Wale
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Is there any function equivalent to repmat in DolphinDB?
This function is pretty useful and is supported in Matlab and Numpy, but I didn't find this function in DolphinDB help page. Is there any equivalent function in DolphinDB?
Ju Piece
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Create an empty vector with certain size in DolphinDB
In Python, I can create an empty list like this:
a = [None] * 5
But in DolphinDB, when I tried to run this:
a = take(NULL, 5)
the interpreter just gave the error message:
Not allowed to create void vector
So how can I create an empty vector with…
Clyx
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-1
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How to upgrade DolphinDB in a Docker container?
I created a container environment with the Docker Image provided by DolphinDB and did some testing. Now I want to upgrade DolphinDB without exiting the container.
I need to kill the DolphinDB process before upgrading. But now I encountered a…
YaN
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