[R] readr to generate tibble from a character matrix

[Ben Tupper]

Hi,

Thanks for this solution!  Very slick! 

I see what you mean about the two calls to as_tibble(). I suppose I could do the following, but I doubt it is a gain...

mm <- lapply(colnames(m), function(nm, m) type.convert(m[,nm], as.is = TRUE), m=m)
names(mm) <- colnames(m)
as_tibble(mm)

# # A tibble: 4 × 5
#       A     B     C     D     E
#   <chr> <chr> <chr> <int> <dbl>
# 1     a     e     i     1  11.2
# 2     b     f     j     2  12.2
# 3     c     g     k     3  13.2
# 4     d     h     l     4  14.2

I'll benchmark these with writing to a temporary file and pasting together a string.

Cheers and thanks,
Ben

On Apr 6, 2017, at 11:15 AM, Ulrik Stervbo <ulrik.stervbo at gmail.com> wrote:
> 
> Hi Ben,
> 
> type.convert should do the trick:
> 
> m %>%
>   as_tibble() %>% 
>   lapply(type.convert) %>% 
>   as_tibble()
> 
> I am not too happy about to double 'as_tibble' but it get the job done.
> 
> HTH
> Ulrik
> 
> On Thu, 6 Apr 2017 at 16:41 Ben Tupper <btupper at bigelow.org <mailto:btupper at bigelow.org>> wrote:
> Hello,
> 
> I have a workflow yields a character matrix that I convert to a tibble. Here is a simple example.
> 
> library(tibble)
> library(readr)
> 
> m <- matrix(c(letters[1:12], 1:4, (11:14 + 0.2)), ncol = 5)
> colnames(m) <- LETTERS[1:5]
> 
> x <- as_tibble(m)
> 
> # # A tibble: 4 × 5
> #       A     B     C     D     E
> #   <chr> <chr> <chr> <chr> <chr>
> # 1     a     e     i     1  11.2
> # 2     b     f     j     2  12.2
> # 3     c     g     k     3  13.2
> # 4     d     h     l     4  14.2
> 
> The workflow output columns can be a mix of a known set column outputs.  Some of the columns really should be converted to non-character types before I proceed.  Right now I explictly set the column classes with something like this...
> 
> mode(x[['D']]) <- 'integer'
> mode(x[['E']]) <- 'numeric'
> 
> # # A tibble: 4 × 5
> #       A     B     C     D     E
> #   <chr> <chr> <chr> <int> <dbl>
> # 1     a     e     i     1  11.2
> # 2     b     f     j     2  12.2
> # 3     c     g     k     3  13.2
> # 4     d     h     l     4  14.2
> 
> 
> I wonder if there is a way to use the read_* functions in the readr package to read the character matrix into a tibble directly which would leverage readr's excellent column class guessing. I can see in the vignette ( https://cran.r-project.org/web/packages/readr/vignettes/readr.html <https://cran.r-project.org/web/packages/readr/vignettes/readr.html> ) that I'm not too far off in thinking this could be done (step 1 tantalizingly says 'The flat file is parsed into a rectangular matrix of strings.')
> 
> I know that I could either write the matrix to a file or paste it all into a character vector and then use read_* functions, but I confess I am looking for a straighter path by simply passing the matrix to a function like readr::read_matrix() or the like.
> 
> Thanks!
> Ben
> 
> Ben Tupper
> Bigelow Laboratory for Ocean Sciences
> 60 Bigelow Drive, P.O. Box 380
> East Boothbay, Maine 04544
> http://www.bigelow.org <http://www.bigelow.org/>
> 
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> and provide commented, minimal, self-contained, reproducible code.

Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
http://www.bigelow.org




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