Yesterday I had the need for a matrix type in Python.
Apparently, a trivial answer to this need would be to use numpy.matrix(), but the additional issue I have is that I would like a matrix to store arbitrary values with mixed types, similarly to a list. numpy.matrix does not perform this. An example is
>>> numpy.matrix([[1,2,3],[4,'5',6]]) matrix([['1', '2', '3'], ['4', '5', '6']], dtype='|S4') >>> numpy.matrix([[1,2,3],[4,5,6]]) matrix([[1, 2, 3], [4, 5, 6]]) As you can see, the numpy.matrix must be homogeneous in content. If a string value is present in my initialization, every value gets implicitly stored as a string. This is also confirmed by accessing the single values
>>> numpy.matrix([[1,2,3],[4,'5',6]])[1,1] '5' >>> numpy.matrix([[1,2,3],[4,'5',6]])[1,2] '6' Now, the Python list type can instead accept mixed types. You can have a list containing an integer and a string, both conserving their type. What I would need is something similar to a list, but operating in a matrix-like behavior.
Therefore, I had to implement my own type. I had two choices for the internal implementation: list containing lists, and dictionaries. Both solutions have shortcomings:
- list of lists require careful synchronization of the various lists’ sizes. Swapping two rows is easy. Swapping two columns is less easy. Removing a row is easy as well.
- dictionaries (with a tuple as a key) are slightly better, but you have to define the limits of your key (for example, you cannot insert element 5,5 if your matrix is 3×3), and they are more complex to use to insert, remove, or swap columns or rows.
Edit: clarification. The concrete reason on why I need this functionality is because I am reading CSV files. Once I collect the values from a CSV file (values that can be string, integers, floats) I would like to perform swapping, removal, insertion and other operations alike. For this reason I need a ‘matrix list’.
My curiosities are:
- do you know if a Python data type providing this service already exists (maybe in a ‘non-battery included’ library out there)?
- why is this data type not provided in the standard library? Too restricted interest maybe?
- How would you have solved this need? Dictionary, list, or another smarter solution?
You can have inhomogeneous types if your
dtypeisobject:I have no idea what good this does you other than fancy indexing, because, as Don pointed out, you can’t do math with this matrix.