Map function to list in Mathematica

Question

I want to map this function (1 - num2/num1)*100 to a list. I used the command below, but the command does not work. Can anyone help?

length = Quantity[List[45, 66, 74.6, 45, 34, 34.4], "Meters"]

The function is:

(1 - #[[1]]/#[[2]])*100 & /@ length

for example1: (1-45/no num)*100 = empty

for example2: (1-66/45)*100 = 46.66

for example3: (1-74/66)*100 = 12.12

&...

Answer 1

Your example has an error: 1-66/45 is negative (so 66/45-1 ?). I guess you want to use BlockMap for this:

list = List[45, 66, 74.6, 45, 34, 34.4];
length = Quantity[#, "Meters"] & /@ list;
BlockMap[(#[[2]]/#[[1]] - 1) 100 &, length, 2, 1] // N

results into

{46.6667, 13.0303, -39.6783, -24.4444, 1.17647}

Or use Ratios:

(Ratios[Quantity[List[45, 66, 74.6, 45, 34, 34.4], "Meters"]] - 1.0) 100