Separate alphabets and numbers
Retina, 14 bytes

O%$`\d|(.)
$#1


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Explanation

O introduces a sorting stage. % tells Retina to apply the transformation to each line separately. $ tells it to sort the matches by the result of the specified substitution.

The regex itself is \d|(.) which either matches a digit, or anything else which is captured into group 1. This is substituted with $#1 which is the number of captures of group 1. That is, the sorting key for digits is 0 and the sorting key for everything else is 1. Since sorting in Retina is stable, this simply moves digits to the left and everything else to the right.