Hi ive had a quick look at your code and simplified it alittle.
Basically it gets the value of transZ from the current obj and sets transY to the same for each obj in the array.

code:
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float $translatez = 0;
string $SelectedObj[] = `ls -sl`;
int $size = size($SelectedObj);

for ($i = 0; $i<$size; $i++)
{
$translatez = `getAttr ($SelectedObj[$i] + ".translateZ")`;
setAttr ($SelectedObj[$i] + ".translateY")$translatez;

}

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Hope this helps