Stefan van der Walt wrote:
On Fri, Sep 22, 2006 at 02:17:57AM -0500, Robert Kern wrote:
According to the putmask docstring:
a.putmask(values, mask) sets a.flat[n] = v[n] for each n where mask.flat[n] is true. v can be scalar.
This would mean that 'w' is not of the right length.
There are 4 true values in m and 4 values in w. What's the wrong
length?
The way I read the docstring, you use putmask like this:
In [4]: x = N.array([1,2,3,4])
In [5]: x.putmask([4,3,2,1],[1,0,0,1])
In [6]: x Out[6]: array([4, 2, 3, 1])
Out[9] and Out[18] should have been the same, but elements 6 and 9 are flipped. It's pretty clear that this is a bug in .putmask().
Based purely on what I read in the docstring, I would expect the above to do
x[0] = w[0] x[6] = w[6] x[9] = w[9] x[11] = w[11]
Since w is of length 4, you'll probably get indices modulo 4:
w[6] == w[2] == -3 w[9] == w[1] == -2 w[11] == w[3] == -4
Which seems to explain what you are seeing.
Yes, this does explain what you are seeing. It is the behavior of Numeric's putmask (where this method came from). It does seem counter-intuitive, and I'm not sure what to do with it. In some sense putmask should behave the same as x[m] = w. But, on the other-hand, was anybody actually using the "modular" indexing "feature" of "putmask". Here are our options: 1) "fix-it" and risk breaking code for people who used putmask and the modular indexing "feature," 2) Get rid of it as a method (and keep it as a function so that oldnumeric can use it.) 3) Keep everything the way it is. -Travis