How to get previous value?

InfluxDB 2
1

I have pretty simple function to apply to inputStream and get outputStream. I was very positive I could accomplish this using flux language, but it turns out getting the previous value in the stream might be a showstopper. Here is the function pseudo-code:

step = (startIntegral - endIntegral) / totalPoints
for(pos = 0; pos < totalPoints, pos++)
{
	if (pos == 0)
		outputStream[pos] = step * (0.5 * inputStream[pos])
	else if (pos == totalPoints - 1)
		outputStream[pos] = outputStream[pos - 1] + (step * (0.5 * inputStream[pos]))
	else
		outputStream[pos] = outputStream[pos - 1] + (step * inputStream[pos])
}

Using the map could have been one option, but how to

  1. get outputStream[pos - 1]? Can I save outputStream[pos] into some temporary variable and then use it?
  2. how to detect first and last points of the stream?
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