# NumberSequence

A NumberSequence represents a series of number values from 0 to 1. The number values are expressed using the `datatype/NumberSequenceKeypoint` type. This type is used in properties of `ParticleEmitter` to indicate properties of particles over their lifetime. In Studio, this data type is edited using a line graph:

The above line graph can be set using a script using the following call to NumberSequence.new:

``````particleEmitter.Transparency = NumberSequence.new{
NumberSequenceKeypoint.new(0, 0), -- (time, value)
NumberSequenceKeypoint.new(.5, .75),
NumberSequenceKeypoint.new(1, 1)
}
``````

## Equality

Two NumberSequences are equivalent if and only if the values of their `datatype/NumberSequenceKeypoint` are equivalent, even if the two NumberSequence would result in similar graphs.

## Evaluation

The NumberSequence type does not have a built-in method for getting the value at a certain time/point because keypoints can have random envelopes. Assuming the envelope values of your keypoints are all 0, you can use the following function to evaluate at a specific time:

``````function evalNS(ns, time)
-- If we are at 0 or 1, return the first or last value respectively
if time == 0 then return ns.Keypoints[1].Value end
if time == 1 then return ns.Keypoints[#ns.Keypoints].Value end
-- Step through each sequential pair of keypoints and see if alpha
-- lies between the points' time values.
for i = 1, #ns.Keypoints - 1 do
local this = ns.Keypoints[i]
local next = ns.Keypoints[i + 1]
if time >= this.Time and time < next.Time then
-- Calculate how far alpha lies between the points
local alpha = (time - this.Time) / (next.Time - this.Time)
-- Evaluate the real value between the points using alpha
return (next.Value - this.Value) * alpha + this.Value
end
end
end
``````

You can use the function above like this:

``````local ns = NumberSequence.new{
NumberSequenceKeypoint.new(0, 0),
NumberSequenceKeypoint.new(.5, .8),
NumberSequenceKeypoint.new(1, 1),
}

print(evalNS(ns, 0))   --> 0
print(evalNS(ns, .25)) --> .4
print(evalNS(ns, .5))  --> .8
print(evalNS(ns, .75)) --> .9
print(evalNS(ns, 1))   --> 1
``````