Hi Tyler, Thanks for your comment. I added this passage in a pull request about a year ago, after we had some problems at a workshop.
I don't remember all the details, but we definitely had problems on multiple machines. I think it may have been Windows computers only. We were using the current version of R at the time. There are some more details in this pull request (closed): https://github.com/swcarpentry/r-novice-inflammation/pull/177 We included this passage simply to provide an easy fix (convert using "as.numeric()") for anyone else who has the same problem. I agree it's best not to introduce any unnecessary concepts too early -- hence we put it in a box and tried to keep it as simple and short as possible; while still including it directly in the course materials in case other instructors have the same problem. I remember it took us a few minutes to find a solution during the workshop, since it wasn't immediately clear what was causing the problem. I tried the example again just now on my Mac, and it worked fine, without the fix. As you point out, the sliced row of the data frame should actually be automatically coerced when you use max(). Sliced columns are already numeric vectors, so no coercion is required there. Re-working the whole lesson to remove this edge case would be difficult, since we would like to keep it consistent with the Python materials, especially using the same inflammation data set. Maybe someone else also has some views here? Best regards, Lukas On Wed, Dec 14, 2016 at 4:09 AM, Tyler Smith <[email protected]> wrote: > Hi, > > I've been working through lesson one in the r-inflammation lesson. It > includes the following passage: > > > ## Forcing Conversion > > > > The code above may give you an error in some R installations, > > since R does not automatically convert a sliced row of a `data.frame` to > a vector. > > (Confusingly, sliced columns are automatically converted.) > > If this happens, you can use the `as.numeric` command to convert the row > of data to a numeric vector: > > > > `patient_1 <- as.numeric(dat[1, ])` > > The example data is entirely numeric, with no missing values, and no > non-numeric columns. In that case, type coercion should work as you > expect. If it doesn't, I would be very surprised if the results depend > on a particular R *installation*. It may be the case that older R > *versions* did different things. But I'm not sure about that. Can > someone confirm which R versions require the explicit conversion of data > to numeric in this example? > > coercion in R does have some ugly corner cases. If this is in fact one > of them, I think it would be a good idea to rework the example so that > it doesn't require this kind of fix. > > Incidentally, columns always work because a column by definition is > composed of a single vector (which therefore has a single type). Rows > can include data from different columns, and thus may have different > types that need to be coerced into the lowest common denominator before > we can use them. This isn't really confusing when you understand how a > dataframe is constructed, but it's perhaps an issue that we don't need > to throw at students in lesson 1. > > Best, > > Tyler > > -- > plantarum.ca > _______________________________________________ > Discuss mailing list > [email protected] > http://lists.software-carpentry.org/listinfo/discuss
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