# Can anyone give an example that is “non-sequential index? Is (red, green, blue) a ”non-sequential index"?

This post says

The insurance risk example illustrates how “time” n need not really be time, but instead can be a sequential indexing of some kind of events.

which use "sequential" to describe "indexing", which seems to indicate that there exists non-sequential indexing.

the definition/explanation on wiktionary is "Not sequential", which gives no more info to help me understand what is "non-sequential index".

Can anyone give an example that is "non-sequential index", is (red, green, blue) a "non-sequential index"?

• There is no reason at all to think that red, green, blue isn't a sequence. There may or may not be a pattern to those colour changes—the sample isn't large enough to tell. On the other hand, 1, 8, 4, 3, 9, 7 is very likely nonsequential. The numbers don't progress in any seeming order or pattern. You've already provided a definition of non-sequential, so it's not clear what's confusing about this. If something can be sequential, it can also be nonsequential. – Jason Bassford Aug 8 '19 at 3:06
• Red, Green, Blue are colors of light, in order of increasing frequency, or decreasing wavelength. – Jasper Aug 8 '19 at 4:21
• @Jasper Thanks man. Would you please give an example to "non-sequential index"? – fu DL Aug 8 '19 at 5:59

It's very likely this is a case of redundancy, where the same idea is expressed in multiple ways. For example "My Big Fat Greek Wedding", where "big" and "fat" mean something similar.

To the extent that sequential means ordered, then most (all?) indexes would be sequential by that definition.

To the extent that sequential might mean consecutively ordered 1,2,3,4 or a,b,c,d then many indexes would not meet that criterion if intermediate values are missing, so it goes 1, 5, 80, 103, 210.

As a data analyst, I can tell you that data can be ordered any number of ways, but whatever "order" you choose it is always "sequential" which literally means that the order follows a sequence.

For example:

• Blue, Green, Red (alphabetical order)
• Red, Blue, Green (descending order according to their Terahertz value on the colour spectrum)
• Blue, Red, Green (by popularity of car colours)

I don't believe there can be such a thing as "non-sequential" ordering, because if any items were listed without a sequence then they would not be any order.

If items were ordered entirely randomly and you were to "index" them as you found them, rather than rearrange them into some kind of order, then it would simply be "an index", so that you could locate them. Arguably though, by creating an index of randomly placed items, you have by doing so created an order. For this reason, I would argue that there is no such thing as "non-sequential indexing", and even that "sequential indexing" is something of a redundancy.

As your quote is defining the concept of "time", it might be worth noting that the term "linear time" is used to describe the nature of time, and while the term "nonlinear" is used, it is considered to be an abstract concept - nothing more than the way people perceive linear time differently.