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Pretty printing of matrices (and multidimensional arrays) #40
Description
Currently the standard Fortran's print *, A prints a 2D array A as a 1D list of numbers. Rather, I would like stdlib to have a function print_array (we can discuss a better name) that would print the array as NumPy:
>>> numpy.arange(10000).reshape(250,40)
array([[ 0, 1, 2, ..., 37, 38, 39],
[ 40, 41, 42, ..., 77, 78, 79],
[ 80, 81, 82, ..., 117, 118, 119],
...,
[9880, 9881, 9882, ..., 9917, 9918, 9919],
[9920, 9921, 9922, ..., 9957, 9958, 9959],
[9960, 9961, 9962, ..., 9997, 9998, 9999]])
or Julia:
julia> B = [1 2; 3 4; 5 6; 7 8; 9 10]
5×2 Array{Int64,2}:
1 2
3 4
5 6
7 8
9 10
Julia can also use nice unicode characters for ... and vertical ... if the array is too large.
Then we should use this function at
stdlib/src/tests/loadtxt/test_loadtxt.f90
Line 21 in ae5591f
Then compilers can perhaps optionally use such print_array as default in the Fortran's language print statement.
Reacted by Ian Giestas Pauli, Milan Curcic, J. Philip Haupt, ZUO Zhihua and Emilio Castro
Activity
jvdp1 commentedon Dec 22, 2019
My preference is for a format like Julia 's one. It would be also a similar format as savetxt.
ivan-pi commentedon Dec 24, 2019
One prior art - Algorithm 892: DISPMODULE, a Fortran 95 module for pretty-printing matrices
https://dl.acm.org/citation.cfm?id=1486531
The code can be downloaded from netlib: http://netlib.org/toms/892.zip
jvdp1 commentedon Dec 24, 2019
Thank you for mentioning this librabry. It seems to be quite complete and flexible. Could we use it (with some modernisations) in
stdlib(license?)?ivan-pi commentedon Dec 25, 2019
Code published in TOMS is under the ACM Software License Agreement which allows usage for non-commercial purposes. I think that it is not compatible with what we want to achieve here.
I know Scipy contains the TOMS 748 algorithm. I checked and it looks like they wrote their own implementation.
certik commentedon Dec 25, 2019
ivan-pi commentedon Dec 25, 2019
I had a look at the DISPMODULE API and it is indeed very nice and flexible supporting different formats (e.g. with a title, numbered rows and columns, precision, separators) and even printing several matrices adjacent to one another.
Taking a peak inside I can say that it would be beneficial to first start work on our own string module to handle conversion of reals/integers/logicals to character strings and some tools to parse format strings.
jvdp1 commentedon Dec 25, 2019
I agree with that. I would also add that I think it would be goood to first take a discussion on the issue #35 , because it will be the same problem for this issue #40 (i.e., printing matrices of different kinds).
Also, since we not use DISPMODULE, we could base this API on those of
savetxt. Afterall, savetxt write a matrix to a file instead to the standard output.utsav-pal commentedon Feb 7, 2026
is this issue still alive