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attr_getter() uses partial matching, which is error-prone/dangerous #460

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huftis opened this Issue Feb 6, 2018 · 3 comments

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huftis commented Feb 6, 2018

Here’s a bug/misfeature is was bitten by today. Basically, I was trying to extract the label associated with each variable in a tibble, using (bascially) map(df, attr_getter("label")).

However, for some of the variables, the value of the labels (note the s) attribute, a ‘> 1’-length vector, were extracted instead. It turned out that this happens when the label attribute is missing. The reason is partial matching on the attribute name, which unfortunately is the default in attr().

It’s to late to change the base attr() function, but partial matching is dangerous ☠️, and I see no reason that this should be the default in attr_getter() too!

To fix this, one only needs to add exact = TRUE in the call to the attr function in get_attr().

Reprex:

library(purrr)
x = c(0, 1, 1, 0)
attr(x, "labels") = c(`0` = "Female", `1` = "Male")
get_label = attr_getter("label")
get_label(x) # Expected output: NULL
#>        0        1 
#> "Female"   "Male"
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hadley commented Feb 7, 2018

Do you want to do a PR?

@hadley hadley added the bug label Feb 7, 2018

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huftis commented Feb 7, 2018

Sure, @hadley, I can try to create a PR.

@hadley hadley added the wip label Feb 7, 2018

huftis added a commit to huftis/purrr that referenced this issue Feb 7, 2018

Don’t use partial matching for attr_getter()
Changed the `attr_getter()` fuction to no longer uses partial matching.
For example, if an `x` object has a `labels` attribute but no `label`
attribute, `attr_getter("label")(x)` will no longer extract the `labels`
attribute (fixes tidyverse#460).

Also added some documentation on the `attr_getter()` function.
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huftis commented Feb 7, 2018

I’ve now added a PR for this issue, @hadley.

@hadley hadley closed this in #461 Feb 7, 2018

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