Use variable under cursor for r.previewDataframe, r.nrow etc.

[andycraig]

When there is no selection, it would be good if the following commands operated on the variable the cursor is on:

r.previewDataframe, r.nrow, r.length, r.head, r.thead, r.names

Details

Consider the following file:

library(ggplot2)
ggplot(iris, aes(Sepal.Width, Sepal.Length)) +
    geom_point()

When the cursor is on iris in line 2, I think it would make sense for r.previewDataframe etc. to act on iris. But calling r.previewDataframe results in the message 'This does not appear to be a dataframe'. Calling r.nrow results in in following appearing in the console:

> nrow(ggplot(iris, aes(Sepal.Width, Sepal.Length)) +)
Error: unexpected ')' in "nrow(ggplot(iris, aes(Sepal.Width, Sepal.Length)) +)"
> nrow(geom_point())
NULL

The reason is that the above commands use getSelection() to decide what to act on. When there is no selection, getSelection() tries to find the 'minimum runnable block of code', which in the above example is lines 2-3.

@MaTo04 Thank you for adding the r.nrow family of commands! Does this suggestion sound okay to you? I don't want to break a use case I haven't thought of.

[andycraig]

Also, under this proposal the cursor would remain where it is, instead of moving down one or more lines.

[andycraig]

Add something to README about using custom R functions as well as nrow etc.

[MaTo04]

Sorry about the late reply. This feature is very helpful but i think it doesn´t work. I tried to follow the instruction but get the error: "ENOENT: no such file or directory, mkdir '/c:/GIT/tmp'". Could you please give a detailed instruction how to use it ?

[andycraig]

Hi @MaTo04, the r.nrow command should still work in the same way it did when you implemented it. Did you try r.nrow or r.previewDataframe?

Here are more detailed instructions:

1. Create a directory temp-r
2. In temp-r, create a file temp.R with the following content:

library(ggplot2)
ggplot(iris, aes(Sepal.Width, Sepal.Length)) +
    geom_point()

3. Use ‘Open Folder...’ and select temp-r
4. Open temp.R
5. Place the cursor on iris (line 2)
6. Use the command R: Preview Dataframe
7. Place the cursor on iris (if it’s not there already)
8. Use the command R: Show number of rows for selected object

If you still get an ENOENT error, that’s probably a bug.

[andycraig]

@MaTo04 I have created a PR with some videos that show the proposed changes (#141).