如何在 KDB 中以二进制格式保存列表/矩阵？

Question

I am trying to save a matrix to file in binary format in KDB as per below:

matrix: (til 10)*/:til 10;
save matrix;

However, I get the error 'type .

I guess save only works with tables? In which case does anyone know of a workaround?

Finally, I would like to read the matrix from the binary file into Python with NumPy , which I presume is just:

import numpy as np
matrix = np.fromfile('C:/q/w32/matrix', dtype='f')

Is that right?

Note: I'm aware of KDB-Python libraries , but have been unable to install them thus far.

Answer 1

save does work, you just have to reference it by name.

save`matrix

You can also save using

`:matrix set matrix;
`:matrix 1: matrix;

But I don't think you'll be able to read this into python directly using numpy as it is stored in kdb format. It could be read into python using one of the python-kdb interfaces (eg PyQ) or by storing it in a common format such as csv.

Answer 2

Another option is to save in KDB+ IPC format and then read it into Python with qPython as a Pandas DataFrame. On the KDB+ side you can save it with

matrix:(til 10)*/:til 10;
`:matrix.ipc 1: -8!matrix;

On the Python side you do

from pandas import DataFrame
from qpython.qreader import QReader

with open('matrix.ipc',"rb") as f:
    matrix = DataFrame(QReader(f).read().data)

print(matrix)