detect() doesn't seem to take a logical vector

[rosseji]

Documentation reads:

.p
A single predicate function, a formula describing such a predicate function,
or a logical vector of the same length as .x

But...

x <- list("foo", "bar")

stringr::str_detect(x,"f")
#> [1]  TRUE FALSE

purrr::detect(x, stringr::str_detect(x,"f"))
#> Error: Don't know how to convert logical into a function

Saw, #330 and see that there might be better functions, but I'm still curious...
A simple work around:

x <- list("foo", "bar")

is_foo <- function(x) stringr::str_detect(x, "f")

purrr::detect(x, is_foo)
#> [1] "foo"

Thanks

sessionInfo()
#> R version 3.4.0 (2017-04-21)
#> Platform: x86_64-apple-darwin15.6.0 (64-bit)
#> Running under: macOS Sierra 10.12.5
#> 
#> Matrix products: default
#> BLAS: /Library/Frameworks/R.framework/Versions/3.4/Resources/lib/libRblas.0.dylib
#> LAPACK: /Library/Frameworks/R.framework/Versions/3.4/Resources/lib/libRlapack.dylib
#> 
#> locale:
#> [1] en_AU.UTF-8/en_AU.UTF-8/en_AU.UTF-8/C/en_AU.UTF-8/en_AU.UTF-8
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#> [1] dplyr_0.7.1     purrr_0.2.2.2   readr_1.1.1     tidyr_0.6.3    
#> [5] tibble_1.3.3    ggplot2_2.2.1   tidyverse_1.1.1
#> 
#> loaded via a namespace (and not attached):
#>  [1] Rcpp_0.12.11     cellranger_1.1.0 compiler_3.4.0   plyr_1.8.4      
#>  [5] bindr_0.1        forcats_0.2.0    tools_3.4.0      digest_0.6.12   
#>  [9] lubridate_1.6.0  jsonlite_1.5     evaluate_0.10.1  nlme_3.1-131    
#> [13] gtable_0.2.0     lattice_0.20-35  pkgconfig_2.0.1  rlang_0.1.1     
#> [17] psych_1.7.5      yaml_2.1.14      parallel_3.4.0   haven_1.1.0     
#> [21] bindrcpp_0.2     xml2_1.1.1       httr_1.2.1       stringr_1.2.0   
#> [25] knitr_1.16       hms_0.3          rprojroot_1.2    grid_3.4.0      
#> [29] glue_1.1.1       R6_2.2.2         readxl_1.0.0     foreign_0.8-69  
#> [33] rmarkdown_1.6    modelr_0.1.0     reshape2_1.4.2   magrittr_1.5    
#> [37] backports_1.1.0  scales_0.4.1     htmltools_0.3.6  rvest_0.3.2     
#> [41] assertthat_0.2.0 mnormt_1.5-5     colorspace_1.3-2 stringi_1.1.5   
#> [45] lazyeval_0.2.0   munsell_0.4.3    broom_0.4.2

[david-jankoski]

i understood the docs as .p should always be a function. Maybe you trying to show a different point but the way you are trying to put purrr::detect() to use could be simply x[stringr::str_detect(x,"f")] right ?

[rosseji]

No, you could be right... I guess that would mean that the documentation should be updated if .p should be a function.

Thanks for the suggestion... Can it be map()ed?

[david-jankoski]

It seems to work so. As far as i understand the error comes when detect passes your logical vector (the result of your call to str_detect) to rlang::as_function. If the guys think a clarification in the docs is worthy i can try my hand at it.
About your question - would be better if you post it on stack overflow, expand on what exactly you are trying to do and i can try and help you.

[lionel-]

It seems like .p should be called .f. I think the original intent is to have mapper semantics, so that this works:

x <- list(
  list(1, foo = FALSE),
  list(2, foo = TRUE),
  list(3, foo = TRUE)
)

detect(x, "foo")
detect_index(x, "foo")

[rosseji]

@david-jankoski Thanks, I'll leave it here. Appreciate the comments thought

And thanks @lionel-, got it.

[jpcompartir]

After changing detect from .p to .f, the documentation still refers to .p for ellipsis

.f | A function, specified in one of the following ways:
... | Additional arguments passed on to .p.

small thing but perhaps worth changing?