[PD] fast way to append to [text] (was: [array quantile] explanation)

[Roman Haefeli]

While still not understanding the purpose of [array quantile], I was
able to achieve this:

> I have n samples and input q while 0 < q < 1. I would like to know
> the
> value x for which q*100 percent samples are smaller than x and (1-
> q)*100 percent bigger. 

Since [text define] got a 'sort'ing feature recently, I am using it to
sort the array. Thus, I migrate the data from [array] to [text], sort
it, transfer it back to the [array]. Once sorted, it is easy to get the
median or any n-quantile. 

I noticed, that [text set] has a time complexity of O(n²), so for
efficiently copying data around, I went [array get] -> [list store] ->
[text fromlist] which has linear time complexity.

I see that [text set] is versatile and thus comes with a cost, but
wouldn't it be nice to still have a way to append to the existing text
with linear time complexity? I've been using [text] a few times and
realize only now that because of this it is only feasible up to a
certain number of lines, since adding lines is getting costlier the
larger the stored text. Only when the whole text can be loaded at once
(which is not always the case), the [list store] work-around can be
used.

I wonder whether a dedicated [text append] could help here, that lacks
the functionality of [text set], but would be fast. Or is it the data
structure used by [text] itself that makes it impossible to append in
linear time?

Roman
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