@pradhyumna85 hotfix to solve ValueError("Data must be 1-dimensional.") in boxcox, in case of non array input x and some lambda.

[pradhyumna85]

What does this implement/fix?

ValueError("Data must be 1-dimensional.") in boxcox (scipy.stats.boxcox), in case of non array input x and some lmbda.

[mdhaber]

Is there a reference issue that explains the problem this is supposed to fix?
Do you have example code that causes the problem in the master branch? That code should be added in the form of a unit test.

[WarrenWeckesser]

I think @pradhyumna85 expects this (for example) to work without raising an exception:

In [3]: boxcox(3.5, lmbda=2)                                                                                     
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-3-4429b9c008d5> in <module>
----> 1 boxcox(3.5, lmbda=2)

~/mc37allpip/lib/python3.7/site-packages/scipy-1.7.0.dev0+d293adb-py3.7-macosx-10.9-x86_64.egg/scipy/stats/morestats.py in boxcox(x, lmbda, alpha)
   1032     x = np.asarray(x)
   1033     if x.ndim != 1:
-> 1034         raise ValueError("Data must be 1-dimensional.")
   1035 
   1036     if x.size == 0:

ValueError: Data must be 1-dimensional.

It makes sense, because when lmbda is given, the function is just a thin wrapper around scipy.special.boxcox. We could simplify this PR by making the first two lines of the function

    if lmbda is not None:
        return special.boxcox(x, lmbda)

That is, move that if statement up from a few lines down. If we're just going to pass the values on to special.boxcox, the parameter validations aren't necessary.

This would change the behavior in a few cases. If any values in x are 0 or negative, stats.boxcox raises an exception. special.boxcox returns nan for those inputs. Also, special.boxcox is a ufunc and will broadcast its arguments, so both x and lmbda can have any shape, as long as the shapes are broadcastable.

If we did this, the docstring would need to be updated to explain that the requirement that x be 1-d and not constant applies only when lmbda is None. Also, no matter what we decide to do, special.boxcox should be added to the "See Also" section of the stats.boxcox docstring.

[pradhyumna85]

I think @pradhyumna85 expects this (for example) to work without raising an exception:

In [3]: boxcox(3.5, lmbda=2)                                                                                     
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-3-4429b9c008d5> in <module>
----> 1 boxcox(3.5, lmbda=2)

~/mc37allpip/lib/python3.7/site-packages/scipy-1.7.0.dev0+d293adb-py3.7-macosx-10.9-x86_64.egg/scipy/stats/morestats.py in boxcox(x, lmbda, alpha)
   1032     x = np.asarray(x)
   1033     if x.ndim != 1:
-> 1034         raise ValueError("Data must be 1-dimensional.")
   1035 
   1036     if x.size == 0:

ValueError: Data must be 1-dimensional.

It makes sense, because when lmbda is given, the function is just a thin wrapper around scipy.special.boxcox. We could simplify this PR by making the first two lines of the function

    if lmbda is not None:
        return special.boxcox(x, lmbda)

That is, move that if statement up from a few lines down. If we're just going to pass the values on to special.boxcox, the parameter validations aren't necessary.

This would change the behavior in a few cases. If any values in x are 0 or negative, stats.boxcox raises an exception. special.boxcox returns nan for those inputs. Also, special.boxcox is a ufunc and will broadcast its arguments, so both x and lmbda can have any shape, as long as the shapes are broadcastable.

If we did this, the docstring would need to be updated to explain that the requirement that x be 1-d and not constant applies only when lmbda is None. Also, no matter what we decide to do, special.boxcox should be added to the "See Also" section of the stats.boxcox docstring.

@WarrenWeckesser Exactly what I meant. As it make sense to boxcox a single value if lmbda is given.

[mdhaber]

Thanks @pradhyumna85! I think this was just fixed in gh-12225.