README.md
In corx: Create and Format Correlation Matrices

corx

‘corx’ aims to be a Swiss Army knife for correlation matrices. Formatting correlation matrices for academic tables can be challenging. ‘corx’ does all the heavy lifting for you. It runs the correlations, and stores all relevant results in a list. Results can be formatted into data.frames which can then easily be rendered into tables in a variety of formats.

You can install the released version of corx from CRAN with:

install.packages("corx")

To try features in development, you can install corx from github

remotes::install_github("conig/corx@devel")

The simplest way to use corx is to supply it with a data.frame, which houses numeric variables.

library(corx)
x <- corx(mtcars)
x
#> corx(data = mtcars)
#> 
#> ----------------------------------------------------------------------------
#>          mpg     cyl    disp      hp    drat      wt    qsec      vs      am
#> ----------------------------------------------------------------------------
#> mpg       -  -.85*** -.85*** -.78***  .68*** -.87***    .42*  .66***  .60***
#> cyl  -.85***      -   .90***  .83*** -.70***  .78*** -.59*** -.81***  -.52**
#> disp -.85***  .90***      -   .79*** -.71***  .89***   -.43* -.71*** -.59***
#> hp   -.78***  .83***  .79***      -   -.45**  .66*** -.71*** -.72***    -.24
#> drat  .68*** -.70*** -.71***  -.45**      -  -.71***     .09    .44*  .71***
#> wt   -.87***  .78***  .89***  .66*** -.71***      -     -.17 -.55*** -.69***
#> qsec    .42* -.59***   -.43* -.71***     .09    -.17      -   .74***    -.23
#> vs    .66*** -.81*** -.71*** -.72***    .44* -.55***  .74***      -      .17
#> am    .60***  -.52** -.59***    -.24  .71*** -.69***    -.23     .17      - 
#> gear   .48**  -.49** -.56***    -.13  .70*** -.58***    -.21     .21  .79***
#> carb  -.55**   .53**    .39*  .75***    -.09    .43* -.66*** -.57***     .06
#>         gear    carb
#> mpg    .48**  -.55**
#> cyl   -.49**   .53**
#> disp -.56***    .39*
#> hp      -.13  .75***
#> drat  .70***    -.09
#> wt   -.58***    .43*
#> qsec    -.21 -.66***
#> vs       .21 -.57***
#> am    .79***     .06
#> gear      -      .27
#> carb     .27      - 
#> ----------------------------------------------------------------------------
#> Note. * p < 0.05; ** p < 0.01; *** p < 0.001

To calculate correlations controlling for other variables, use the ‘z’ argument.

x <- corx(mtcars, z = wt, caption = "Correlations controlling for weight")
x
#> corx(data = mtcars, z = wt, caption = "Correlations controlling for weight")
#> 
#> Correlations controlling for weight
#> -------------------------------------------------------------------------------
#>         mpg     cyl    disp      hp  drat    qsec      vs     am   gear    carb
#> -------------------------------------------------------------------------------
#> mpg      -   -.56**    -.34  -.55**   .18   .55**    .44*    .00   -.06   -.40*
#> cyl  -.56**      -   .72***  .68***  -.33 -.74*** -.73***    .04   -.07     .34
#> disp   -.34  .72***      -   .60***  -.24 -.62*** -.57***    .07   -.10     .04
#> hp   -.55**  .68***  .60***      -    .04 -.80*** -.57***   .39*   .42*  .69***
#> drat    .18    -.33    -.24     .04    -     -.05     .08   .43*  .50**     .34
#> qsec  .55** -.74*** -.62*** -.80***  -.05      -   .79*** -.49**  -.39* -.65***
#> vs     .44* -.73*** -.57*** -.57***   .08  .79***      -   -.36*   -.17   -.44*
#> am      .00     .04     .07    .39*  .43*  -.49**   -.36*     -  .67***   .54**
#> gear   -.06    -.07    -.10    .42* .50**   -.39*    -.17 .67***     -   .71***
#> carb  -.40*     .34     .04  .69***   .34 -.65***   -.44*  .54** .71***      - 
#> -------------------------------------------------------------------------------
#> Note. * p < 0.05; ** p < 0.01; *** p < 0.001

Sometimes you only want the relationships for a subset of variables. Asymmetric matrices are useful in these instances. The arguments ‘x’ and ‘y’ can be used to achieve this. ‘x’ sets row variables, ‘y’ sets column variables.

x <- corx(mtcars, x = c(mpg, wt))
x
#> corx(data = mtcars, x = c(mpg, wt))
#> 
#> -------------------
#>         mpg      wt
#> -------------------
#> mpg      -  -.87***
#> wt  -.87***      - 
#> -------------------
#> Note. * p < 0.05; ** p < 0.01; *** p < 0.001

x <- corx(mtcars,
          x = c(mpg, wt),
          y = c(hp, gear, am))
x
#> corx(data = mtcars, x = c(mpg, wt), y = c(hp, gear, am))
#> 
#> ---------------------------
#>          hp    gear      am
#> ---------------------------
#> mpg -.78***   .48**  .60***
#> wt   .66*** -.58*** -.69***
#> ---------------------------
#> Note. * p < 0.05; ** p < 0.01; *** p < 0.001

Users can further customise the table for publication. For instance, the numbers of significance stars can be changed, the area above the diagonal omitted, and captions and notes added.

x <- corx(mtcars[,1:5],
          stars = c(0.05),
          triangle = "lower",
          caption = "An example correlation matrix")
x
#> corx(data = mtcars[, 1:5], stars = c(0.05), triangle = "lower", 
#>     caption = "An example correlation matrix")
#> 
#> An example correlation matrix
#> -------------------------------
#>             1     2     3     4
#> -------------------------------
#> 1. mpg     -                   
#> 2. cyl  -.85*    -             
#> 3. disp -.85*  .90*    -       
#> 4. hp   -.78*  .83*  .79*    - 
#> 5. drat  .68* -.70* -.71* -.45*
#> -------------------------------
#> Note. * p < 0.05

We can also add in descriptive statistics easily.

x <- corx(mtcars[,1:5],
          stars = c(0.05, 0.01, 0.001),
          triangle = "lower",
          caption = "An example correlation matrix",
          describe = c(M = mean, SD = sd, kurtosis))
x          
#> corx(data = mtcars[, 1:5], stars = c(0.05, 0.01, 0.001), triangle = "lower", 
#>     caption = "An example correlation matrix", describe = c(M = mean, 
#>         SD = sd, kurtosis))
#> 
#> An example correlation matrix
#> -------------------------------------------------------------
#>               1       2       3      4      M     SD kurtosis
#> -------------------------------------------------------------
#> 1. mpg       -                          20.09   6.03     2.80
#> 2. cyl  -.85***      -                   6.19   1.79     1.32
#> 3. disp -.85***  .90***      -         230.72 123.94     1.91
#> 4. hp   -.78***  .83***  .79***     -  146.69  68.56     3.05
#> 5. drat  .68*** -.70*** -.71*** -.45**   3.60   0.53     2.44
#> -------------------------------------------------------------
#> Note. * p < 0.05; ** p < 0.01; *** p < 0.001

To add descriptive columns describe can be set to any combination of the following values: c(“mean”,“sd”,“median”,“iqr”,“var”,“skewness”,“kurtosis”).

Alternatively, you can pass a list of named functions:

x <- corx(mtcars[,1:8], describe = list(Mean = function(x) mean(x),
                                        SD = function(x) sd(x)))
x
#> corx(data = mtcars[, 1:8], describe = list(Mean = function(x) mean(x), 
#>     SD = function(x) sd(x)))
#> 
#> ---------------------------------------------------------------------------
#>          mpg     cyl    disp      hp    drat      wt    qsec      vs   Mean
#> ---------------------------------------------------------------------------
#> mpg       -  -.85*** -.85*** -.78***  .68*** -.87***    .42*  .66***  20.09
#> cyl  -.85***      -   .90***  .83*** -.70***  .78*** -.59*** -.81***   6.19
#> disp -.85***  .90***      -   .79*** -.71***  .89***   -.43* -.71*** 230.72
#> hp   -.78***  .83***  .79***      -   -.45**  .66*** -.71*** -.72*** 146.69
#> drat  .68*** -.70*** -.71***  -.45**      -  -.71***     .09    .44*   3.60
#> wt   -.87***  .78***  .89***  .66*** -.71***      -     -.17 -.55***   3.22
#> qsec    .42* -.59***   -.43* -.71***     .09    -.17      -   .74***  17.85
#> vs    .66*** -.81*** -.71*** -.72***    .44* -.55***  .74***      -    0.44
#>          SD
#> mpg    6.03
#> cyl    1.79
#> disp 123.94
#> hp    68.56
#> drat   0.53
#> wt     0.98
#> qsec   1.79
#> vs     0.50
#> ---------------------------------------------------------------------------
#> Note. * p < 0.05; ** p < 0.01; *** p < 0.001

Corx objects can be passed directly to papaja::apa_table(), or knitr::kable().

corx(mtcars[, 1:5], triangle = "lower", describe = c(mean, sd)) |>
  knitr::kable(caption = "My correlation matrix")

| | 1 | 2 | 3 | 4 | mean | sd | |:---------|:-----------|:-----------|:-----------|:---------|:-------|:-------| | 1. mpg | - | | | | 20.09 | 6.03 | | 2. cyl | -.85*** | - | | | 6.19 | 1.79 | | 3. disp | -.85*** | .90*** | - | | 230.72 | 123.94 | | 4. hp | -.78*** | .83*** | .79*** | - | 146.69 | 68.56 | | 5. drat | .68*** | -.70*** | -.71*** | -.45** | 3.60 | 0.53 |

My correlation matrix

There are many useful functions for plotting correlation matrices. ‘corx’ contains a plot function which uses the ‘ggcorrplot’ package.

plot(x)

Multidimensional scaling enables similarities between variables to be converted to 2D distances. This lets us visualise how variables cluster together.