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Suggested convenient function: move column order #4668
Description
In my daily development I wrote some convenient functions. There is nothing fancy in them, but I feel they are quite useful in data analysis. So I'm wondering if they can be useful to others and be included as a part of data.table.
move column order
I may generate some new column and it will be located at the end of the table. I want to move it to around the relevant columns so it's easier to compare/investigate them. It's hard to write a full column order vector for this manually, nor will the "move some columns to front" option in setcolorder help on this.
move_cols <- function(dt, cols_to_move, position = "after", anchor) {
stopifnot(position %in% c("before", "after"))
# we always split columns without the moving subset into left, anchor, right, then insert the moving subset before or after anchor
original_cols <- names(dt)
anchor_location <- which(original_cols == anchor)
left_cols <- setdiff(original_cols[1:(anchor_location - 1)], cols_to_move)
right_cols <- setdiff(original_cols[(anchor_location + 1):length(original_cols)], cols_to_move)
new_cols <- switch(position,
before = c(left_cols, cols_to_move, anchor, right_cols),
after = c(left_cols, anchor, cols_to_move, right_cols))
setcolorder(dt, new_cols)
}
dt <- data.table(mtcars)
# note the parameter order is easy to read
move_cols(dt, "wt", "after", "disp")[]
Activity
ColeMiller1 commentedon Aug 10, 2020
Same as #4358?
dracodoc commentedon Aug 10, 2020
Yes this is the same request. Glad to see similar request.
Mine has the implementation done as a simple wrapper on setcolorder. Adding parameter to setcolorder is another possible interface.
My implementation though is name based, as I prefer to use column name which is more robust to change in data. In this aspect adding parameter to setcolorder may means it need to support column index, which need another implementation (the idea is similar and simple). I'd love to implement it too if needed.
ColeMiller1 commentedon Aug 11, 2020
Would you mind closing this and adding to the other issue? There may be more input on API - mainly
move_cols(dt, "wt", "after", "disp")vs.setcolorder(dt, "wt", .after = "disp"). The implementation could be similar to what you provided.setcolorderaccepts integer or character vectors - the other FR would need to support it as well.mrdwab commentedon Aug 11, 2020
@dracodoc Just a heads up: I think you need to modify your function for cases when you're moving before the first column or after the last column:
Also, just for fun, there's also my
moveMefunction that can easily be modified to work likemove_colswithsetcolorder. It doesn't work with values with spaces though--something I've been meaning to work on.jangorecki commentedon Aug 11, 2020
Better new arg than new function
dracodoc commentedon Aug 11, 2020
Yes, thanks for pointing out this. I often feel R's treatment for indexing is not optimal in these cases, i.e
vec[1:0]should just return NULL then everything will be fine.If there is a plan to add the feature to setcolorder, I'd love to implement a PR for review, including the first/last bug fixed, and supporting column index.
dracodoc commentedon Aug 11, 2020
I created a PR at #4669.