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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How to turn matrix into tuple?
How can I convert a double matrix into a tuple, do I have to construct an empty tuple first, and then use a loop to add each column of the matrix ? Is there an easier way?
user15518852
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Find missing data in consecutive numbers
Table has an index , it starts from 1 and the rest will be sequentially numbered, and now there are missing data that cause discoontinuity, how can I write sql to find the serial number missing, such as the following, by serial number sorting line…
damie
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Are there any statements that can directly export the table creation scripts?
We have tables in the background. Are there any statements that can directly export the table creation script? We want to create a new table on another machine.
user15518852
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How to select unique elements in a column of the table in DolphinDB?
If there are duplicated elements in a column, how to select the unique elements in a column in DolphinDB?
user15518852
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Does dolphindb support weighted least squares regression “wls”?
I have a request on weighted least squares. Does dolphindb support weighted least squares regression “wls”? How to use it?
user15518852
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how long will the python API take for the same query compared with c/c++?
I would like to ask, for the same back-end ddb, if the query result is 1G, how long will the access time with Python increase compared to using c/c++? I don't know if there is any test in this area.
user15518852
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Which function in DolphinDB is similar to the lag operation?
For example, the original data looks like this:
ID
x
1
10
2
11
3
12
4
13
5
14
6
15
7
16
8
17
9
18
10
19
After doing lag operation on the ID column, the following results are…
user15518852
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Does DolphinDB have a function to calculate the correlation between two columns?
I want to calculate the correlation between two columns, does DolphinDB have such functions? It seems that the function "corr" only apply to the vector. I get the error as below:
corr(x, y) => getDoubleConst method not supported
winnie
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How to get the label column from a table which is converted by a matrix which is obtained by the pivot function?
I get the matrix by the function pivot, then I transfer it into a table by the function table. I find the table lost the label column. How to save the label column in this table?
The example codes are shown as…
user15504166
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How to select the multiple outputs from a function?
I define a function by the following code:
def func(Open,High,Low,Close,20)
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return x,y
There are two return results in the function “func()”, and I want to select these two results in one select clause. I write a statement…
damie
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How to quickly identify whether there is any blockage during streaming data processing?
In the cluster, I create multiple streaming tables together with multiple subscriptions using different topics. But the processing of several subscriptions is obviously delayed. How can I quickly identify whether there is any blockage during…
damie
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Why is the timestamp inserted by the function “now()” shown as 1992?
I write the following scripts, but the timestamp is wrong:
t=table(10:0, `sym`datetime, [SYMBOL,DATETIME]);
insert into t values("abc",now())
t
sym datetime
abc 1992.07.14T09:35:43
print select now()
([2021.08.09T10:11:24.080])
The shown time is…
user15504166
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Do the log files which are allocated on agent, controller and datanode can be compressed and archived?
If a file is written all the time, it will be time-consuming to download and open while troubleshooting. I hope there is a function to compress and archive these files according to the date and size.
user15504166
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How to define a shared table inside a function?
I want to define a shared table inside a function, It works if I use share(table,`sharedTable). I wonder why can't I put the “share table as sharedTable” statement in a function?
user15518852
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Does DolphinDB support modifying the field type in a dfs table?
I create a dfs table. The script is as below:
db = database("dfs://valuedb", VALUE, 2000.01M..2016.12M)
schemaTable = table(1:0, `symbol`time`price, [STRING, TIMESTAMP, DOUBLE])
pt = db.createPartitionedTable(schemaTable, `pt, `time)
Now, I want to…
user15518852