Using any cumulative custom function

[jyrikuusik]

Is it possible with dplyr or with other R package use any custom cumulative function (i.e. cumulative linear trend, ) for given longitudinal data frame, with next variables:
x - numerical or categorical variable
ID - object ID
t - tenure (1,2,....)
For instance I would like to have linear trend for x[1:2], x[1:3], x[1:4],....for each ID and tenure
in the flexible way (with some dplyr function)

[mara]

I'm not sure I totally understand your scenario, but are you talking about something akin to window functions?

Window functions

You might also look at the window functions and functionality provided by the tsibble package
https://tsibble.tidyverts.org/articles/window.html
GIF from Earo Wang's talk on tsibble at rstudio::conf(2019)

[jyrikuusik]

Many thanks! Yes, I was thinking about "stretch_dbl"

[cderv]

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[jyrikuusik]

Hi. I can not see where I can close my question

[mara]

Here's a GIF of how you do it (I selected and then de-selected so that you can do it yourself)