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 insert rows with NULL values to a DolphinDB table?
I want to insert a record to a table with columns “A”, “B”, and “C”. In this record, the “B” column contains a NULL value. When I used table(12 as A, NULL as B, 13 as C), I encountered an error: Not allowed to create void vector. Does anyone know…
carbonhydrate
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How to pass a variable to DolphinDB’s panel function as the metrics parameter?
As shown in the following script, I’d like to use a variable containing a list of column names as the metrics parameter in DolphinDB’s panel function.
fields=`factor1`factor2`factor3`factor4
res1=panel(tmp.quarter, tmp.order_book_id, fields, time, ,…
Eva Gao
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Error when using "moving" on a matrix input in DolphinDB
I want to calculate the moving average for each column of a matrix in DolphinDB. But I encountered an error when using higher order function moving(avg, m, w), which is shown in the following figure.
However, the function mavg(m, w) works fine…
Eva Gao
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Understanding the output of "createWindowJoinEngine" with parameter window set to 0:0
I'm having trouble comprehending the output of the createWindowJoinEngine function in the context of special windows (window=0:0), as shown in the following diagram. Could you please provide a detailed explanation?
Eva Gao
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Exponentiation with Negative Bases in DolphinDB
As shown in the following script, I want to raise all elements of x to the power of y.
x=[-3,-2,3,3,3,4]
y=[1/3.0,0.334,0.334,1/3,1/3.0,2]
pow(x,y)
I noticed that the result contains NULL values for negative numbers as the base:
Is it a specific…
JaneYe
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Errors "IO error type 6" and "IO error type 13" occur when DolphinDB Python API is used
When using DolphinDB Python API to query data from DolphinDB database, I often encounter two types of errors: Failed to parse the incoming object with IO error type 6 or Failed to parse the incoming object with IO error type 13.
Here's the…
zhihengqu
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DolphinDB: How to calculate the difference between two rows in a table?
I have a table containing the four columns “order_book_id”, “date”, “Q”, and “revenue”. I want to perform the following operations:
Group the table by “order_book_id” and “date”.
Verify if the values of column "Q" are equal to 1 within each group…
Smalllpotato
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Why can’t I see the database list in the DolphinDB web interface?
I am using the DolphinDB web interface with the DB_READ privilege. However, I cannot access the databases in the web interface. I am wondering if it is because that I’m not granted the DB_MANAGE permission.
Can anyone shed some light on this issue?…
molddd123
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Metaprogramming for binary functions in DolphinDB
When I handled a SELECT statement involving a binary function, such as select func(a,b) from tb, the sqlCol function can not be used. Does anyone know any alternative metaprogramming techniques available to address this situation?
Claire
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Error reported when using sma in a SQL query: X must be a numeric vector
Here is my script:
def ma process(data table){
cols = open'high'low'close' volume'amount'vwap
base_table = select trade date, symbol from data_table
for(col in cols){
print(col)
data = select trade_date, symbol, sma(col,5)…
carbonhydrate
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1 answer
Error with MTW: in insert: thread is exiting
When I used MultiThreadTableWriter provided by the dolphindb Python API to write data into a DolphinDB table, an error was reported: in insert: thread is exiting, which is shown as follows.
I don’t know what might have caused this…
YaN
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DolphinDB: the difference between percentile and quantile?
The functionality of percentile and quantile described in the DolphinDB user manual is similar. The main difference lies in the format of the input parameters, for example, percentile(a, 25) and quantile(a, 0.25). Am I right in understanding this?
carbonhydrate
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1 answer
How to generate minute-level data from Level 2 streaming data?
I would like to know if DolphinDB provides any available script for generating minute-level data (such as OHLC bars) from Level 2 streaming data. And since OHLC bars are generated based on the fixed time intervals, it is challenging to handle the…
Polly
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How to concatenate two tuples in DolphinDB?
I want to concatenate two tuples in the way similar to concatenating vectors. For example, I have two tuples: a=(1,2,3) and b=(4,5,6), and I want to use join to obtain re=(1,2,3,4,5,6). However, the output is (1,2,3,(4,5,6)), which is same as the…
Polly
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How to reduce memory usage on DolphinDB nodes?
I found that a large amount of memory is consumed by my data nodes, even though there are no jobs running.
Does anyone know the possible causes of this problem? And I would greatly appreciate it if someone could share some best practices for how to…
Smalllpotatoo1
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