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incrementing elements of a SparseArray

• To: mathgroup at smc.vnet.net
• Subject: [mg123681] incrementing elements of a SparseArray
• From: Matt Enlow <mattenlow at gmail.com>
• Date: Thu, 15 Dec 2011 04:55:37 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• Reply-to: mattenlow at gmail.com

Hi,

I am creating a very large 2-dimensional SparseArray ("M") by starting with
an empty one (all zeros) and iterating a tight loop, which increments a
different element of M each time. In the end result, M will still be mostly
zeros, but some entries will be anywhere from 1 to about 50. I have a way
to do it, but I feel as though there is probably a better way.

Originally I thought I could use MapAt, but when I use it on a SparseArray,
it returns a "Normal" array, which I don't want to keep having to convert
back to a SparseArray every time. My "fix" was to create a new SparseArray
that only has a 1 in the position I want to increment (zeros everywhere
else), then add it to M. Again, this works, but feels inefficient. Is there
a simpler and/or more efficient way to do this?

Thanks in advance,

Matt Enlow

• Follow-Ups:
  • Re: incrementing elements of a SparseArray
    • From: Leonid Shifrin <lshifr@gmail.com>
  • Re: incrementing elements of a SparseArray
    • From: DrMajorBob <btreat1@austin.rr.com>