CODEWITHSUNDEEP
pythoncython
firdaus
firdaus

Reputation: 541

Sorting in cython

I'm new to cython, and I'm trying to write an algorithm that needs to repeatedly sort partially sorted arrays. It appears that python's standard sort (timsort?) is quite good for this, but I haven't figure out how to call this function from inside a cythonized function.

Namely, I want to do something like:

cdef void myfunc(double* y) nogil:
    double *y_sort = sort(y)

Any pointers on how to do this would be appreciated.

Upvotes: 2

Views: 2947

Answers (1)

J.J. Hakala
J.J. Hakala

Reputation: 6214

Standard C library provides qsort

# from libc.stdlib cimport qsort
# ... declaring "const void *" type seems problematic

# https://stackoverflow.com/questions/8353076/how-do-i-pass-a-pointer-to-a-c-fun$
cdef extern from "stdlib.h":
    ctypedef void const_void "const void"
    void qsort(void *base, int nmemb, int size,
                int(*compar)(const_void *, const_void *)) nogil

cdef int mycmp(const_void * pa, const_void * pb):
    cdef double a = (<double *>pa)[0]
    cdef double b = (<double *>pb)[0]
    if a < b:
        return -1
    elif a > b:
        return 1
    else:
        return 0

cdef void myfunc(double * y, ssize_t l) nogil:
    qsort(y, l, sizeof(double), mycmp)

If the array is "almost-sorted", then insertion sort might be better: https://stackoverflow.com/a/2726841/5781248

Upvotes: 4

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