Factors don't always work as intended

[mattansb]

library(correlation)
#> Warning: package 'correlation' was built under R version 4.2.3

data("mtcars")

mtcars$cyl <- factor(mtcars$cyl)

correlation(mtcars, 
            select = c("mpg", "cyl"), 
            include_factors = TRUE)
#> # Correlation Matrix (pearson-method)
#> 
#> Parameter1 | Parameter2 |     r |         95% CI | t(30) |         p
#> --------------------------------------------------------------------
#> mpg        |      cyl.4 |  0.80 | [ 0.63,  0.90] |  7.35 | < .001***
#> mpg        |      cyl.6 | -0.03 | [-0.38,  0.32] | -0.17 | 0.866    
#> mpg        |      cyl.8 | -0.74 | [-0.87, -0.53] | -6.06 | < .001***
#> cyl.4      |      cyl.6 | -0.38 | [-0.65, -0.04] | -2.27 | 0.061    
#> cyl.4      |      cyl.8 | -0.64 | [-0.81, -0.37] | -4.54 | < .001***
#> cyl.6      |      cyl.8 | -0.47 | [-0.70, -0.14] | -2.89 | 0.021*   
#> 
#> p-value adjustment method: Holm (1979)
#> Observations: 32

Fails

correlation(mtcars, 
            select = c("mpg"), 
            select2 = c("cyl"), 
            include_factors = TRUE)
#> Warning: The table is empty, no rows left to print.
#> Can't export table to 
#>   text
#>   , data frame is empty.

cyl is in Parameter1 not in Parameter2:

correlation(mtcars, 
            select = c("mpg"), 
            select2 = c("cyl", "am"), 
            include_factors = TRUE)
#> # Correlation Matrix (pearson-method)
#> 
#> Parameter1 | Parameter2 |     r |         95% CI | t(30) |       p
#> ------------------------------------------------------------------
#> mpg        |         am |  0.60 | [ 0.32,  0.78] |  4.11 | 0.001**
#> cyl.4      |         am |  0.47 | [ 0.15,  0.71] |  2.94 | 0.019* 
#> cyl.6      |         am |  0.02 | [-0.33,  0.37] |  0.13 | 0.896  
#> cyl.8      |         am | -0.47 | [-0.71, -0.15] | -2.94 | 0.019* 
#> 
#> p-value adjustment method: Holm (1979)
#> Observations: 32

^{Created on 2023-07-09 with reprex v2.0.2}