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jakirkham opened this issue Jul 26, 2017 · 6 comments
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nonzero on arrays of characters with whitespace #9462

jakirkham opened this issue Jul 26, 2017 · 6 comments

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@jakirkham
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It seems that whitespace in a character array is treated as if it is zero. An example of this is shown below with details about the environment. This seems to match up with how character arrays work. Still this seems a bit surprising from a Python perspective. Am trying to understand if this is intentional and also if there is an builtin element-wise operator that we can use to reproduce this behavior.

Code snippet:

In [1]: import numpy as np

In [2]: s = np.array(list("hello world"))

In [3]: s
Out[3]: 
array(['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd'],
      dtype='|S1')

In [4]: s.nonzero()
Out[4]: (array([ 0,  1,  2,  3,  4,  6,  7,  8,  9, 10]),)

Environment: 

name: np2
channels:
- conda-forge
- defaults
dependencies:
- appnope=0.1.0=py27_0
- backports.shutil_get_terminal_size=1.0.0=py27_1
- blas=1.1=openblas
- ca-certificates=2017.4.17=0
- certifi=2017.4.17=py27_0
- decorator=4.1.1=py27_0
- enum34=1.1.6=py27_1
- ipython=5.4.1=py27_0
- ipython_genutils=0.2.0=py27_0
- libgfortran=3.0.0=0
- ncurses=5.9=10
- numpy=1.13.1=py27_blas_openblas_200
- openblas=0.2.19=2
- openssl=1.0.2l=0
- pathlib2=2.3.0=py27_0
- pexpect=4.2.1=py27_0
- pickleshare=0.7.3=py27_0
- pip=9.0.1=py27_0
- prompt_toolkit=1.0.14=py27_0
- ptyprocess=0.5.2=py27_0
- pygments=2.2.0=py27_0
- python=2.7.13=1
- readline=6.2=0
- scandir=1.5=py27_1
- setuptools=36.2.2=py27_0
- simplegeneric=0.8.1=py27_0
- six=1.10.0=py27_1
- sqlite=3.13.0=1
- tk=8.5.19=1
- traitlets=4.3.2=py27_0
- wcwidth=0.1.7=py27_0
- wheel=0.29.0=py27_0
- zlib=1.2.11=0
- pip:
  - backports.shutil-get-terminal-size==1.0.0
  - ipython-genutils==0.2.0
  - prompt-toolkit==1.0.14
@jakirkham jakirkham mentioned this issue Jul 27, 2017
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@jakirkham
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Would be good to hear your thoughts on this one too, @eric-wieser, if you have time.

@eric-wieser
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I was about to ask about what you just reported in #9479 anyway, so there's obviously something screwy going on here

@eric-wieser
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Seems to be by design:

static npy_bool
STRING_nonzero (char *ip, PyArrayObject *ap)
{
    int len = PyArray_DESCR(ap)->elsize;
    int i;
    npy_bool nonz = NPY_FALSE;
    npy_bool seen_null = NPY_FALSE;

    for (i = 0; i < len; i++) {
        if (*ip == '\0') {
            seen_null = NPY_TRUE;
        }
        else if (seen_null || !Py_STRING_ISSPACE(*ip)) {
            nonz = NPY_TRUE;
            break;
        }
        ip++;
    }
    return nonz;
}

@eric-wieser
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See #9848

@jakirkham
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Seems you have opened issue ( #9875 ), which more generally captures the problem here. Should we close this out and follow along on that issue instead?

@mattip
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mattip commented Apr 29, 2019

Duplicate of #9875, please reopen if I misunderstood

@mattip mattip closed this as completed Apr 29, 2019
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@eric-wieser @mattip @jakirkham