Informant is my friend that has grown up in Taiwan and Canada, while also studying in LA.
In almost every modern apartment in Taiwan, they will usually have the 4th floor, but older buildings will not have the 4th floor because the number 4 is a homophone to the word death. 死(si) death and 四(si) four sound similar so to prevent people from living on the “floor of death” they got rid of the 4th floor. It is especially the case in Hospitals. There are no floors or rooms with the number 4, no one would want to stay in a hospital room or floor that has anything that reminds them of death!
I think this is very similar to the American unlucky number 13, although this seems to be more prevalent in Taiwan. Although not seen as much in newer buildings and such, it is still seen in the older buildings. Just goes to show that with time, some superstitions disappear in many ways.