Compare list elements with a catch: reciprocal comparisons must occur FIRST…also element order matters

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I am writing a script in Jython/Python for image analysis (using ImageJ). My goal is to compare the images to eachother…

(edit for clarity: Each element in the list must be compared to every other element, but self-comparisons are not allowed.)

…but I have some specific requirements. These requirements are based on the fact that I’m using a predefined plugin.

For example:

i magefiles = ["A", "B", "C"]

First: order matters. "A" vs "B" is different than"B" vs. “A”.

Second: the list is of variable size, based on user input. In this example, the user has input 3 files: A,B,C, but the code needs to accomodate instances where the number of elements does not equal three.

Third: self-comparison is not allowed. Ie: "A" vs. "A" cannot occur.

Fourth: I would like the comparisons be reciprocated before moving onto the next element. For example:

"A" vs "B" then "B" vs "A" rather than "A" vs "B" then "A" vs "C"

Fifth: I ultimately need to access the elements in the form of a string (requirement due to calling user-defined variables into a preexisting plugin).

For clarity, the comparisons that must be made are:

"A" vs "B"
"B" vs "A"
"A" vs "C"
"C" vs "A"
"B" vs "C"
"C" vs "B"

I’m able to produce a code that does everything except the FOURTH requirement…that is reciprocal comparisons first. But I’m really stuck on how to make the the order of comparisons what I want. Here’s the current working snipped, that does not meet my 4th requirement.

from ij import IJ  #using Jython scripting in the ImageJ program

`imagefiles = ["A", "B", "C"]`

for index, imgs in enumerate(imagefiles):

    for s, secondimage in enumerate(imagefiles):
        if s != index:
  "PluginFE", "element1="+imgs+" element2="+secondimage) #this calls the plugin (PluginFE) within the ImageJ program)

I’m trying to think about how to accomplish the comparison order requirement…and coming up with something like this:

for imgs in imagefiles:

for index in range(len(imagefiles)):
  if index < len(imagefiles):"PluginFE", "element1="+imgs+"element2="+imagefiles[index+1])

but this fails with the error

IndexError: index out of range: 3

I understand the error,and the problem…I just can’t figure out how to work around. I’m still pretty new to coding, so I may be missing an obvious python function!

Thanks for any input


It looks to me like your first bit of Python has the right idea. I am not clear on what the point of posting the second bit is. I think you should be able to get what you want this way.

from ij import IJ
imagefiles = ["A", "B", "C"]
for index1, img1 in enumerate(imagefiles):
    for index2, img2 in enumerate(imagefiles):
        if index2 > index1:
  "PluginFE", "element1="+img1+" element2="+img2)
  "PluginFE", "element1="+img2+" element2="+img1)