R readr single col_types

Question

Is it possible within readr package to read in data and specify a single data type across all columns? Similar to base::read.table with colClasses = "character" or using the as.is argument.

Unless the task, data headers, file encoding, etc are well defined ahead of analysis I prefer to write my loaders without changing the datatypes and then process the schema later downstream. Always open to suggestion on how other folks think about things.

To set all the columns to the same type, read 1 line with `nmax = 1` to get the number of columns, then read the whole thing with `col_types = paste(rep("c", ncol), collapse = "")` (for "character"). — Gregor Thomas, Jul 30 '15 at 21:45
I think asking if **readr** has the ability to recycle column specifications in the same way as `colClasses` in `read.table` is pretty reasonable. I don't see a compact, direct way to do it, but I think it would make a good feature request on github. — joran, Jul 30 '15 at 21:52
Thanks, yes i checked out the docs as well as the col_types.R file on github but nothing jumped out at me. I agree there are certainly work around but would probably just default back to base functions rather than doing any sort of "trickery" (for reasons of maintainability). — gbartusk, Jul 30 '15 at 21:55
FWIW, I sort of doubt that Hadley would like the idea of a fully recycled column specification, but he might be open to adding a compact, direct way to tell **readr** to just read everything as character (or another single type). — joran, Jul 30 '15 at 22:09
In principle, you don't need to worry about `column_types` because they will be imputed from the first 30 rows on the input. For details, check `?read_table` In case you really want to specify a single data type across all columns, Gregor's answer is pretty good. — rafa.pereira, Sep 28 '15 at 15:44

score 8 · Answer 1 · answered Oct 22 '15 at 19:12

8

As of readr 0.2.2 we can do something like this to read a csv with all columns as character:

read_csv("path/to/file",col_types = cols(.default = col_character()))

answered Oct 22 '15 at 19:12

joran

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score 3 · Accepted Answer · answered Jul 30 '15 at 21:51

Converting my comment to answer. No, this isn't built-in (at this point), the documentation of the col_types is quite clear about its capabilities, this isn't one of them. Given the way col_types works, implementing this would probably require a brand new argument since a feature is that a "short" col_types will be used to restrict the number of columns read.

However, you could write a wrapper:

read_table_asis = function(...) {
    n_cols = ncol(read_table(..., n_max = 1))
    read_table(..., col_types = paste(rep("c", n_cols), collapse = ""))
}

ended up going with this solution, despite by reluctance, since it was fewer keystrokes than writing out all the read.table options... thanks! — gbartusk, Aug 27 '15 at 15:35

R readr single col_types

2 Answers2