Visualize correlation matrix using symnum function

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<li>Graph of correlation matrix using symnum function</li>
<li>Conclusions</li>
<li>Infos</li>
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This article describes how to make a graph of correlation matrix in R. The R symnum() function is used. It takes the correlation table as an argument. The result is a table in which correlation coefficients are replaced by symbols according to the degree of correlation.

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<i class="fa - fa-cogs fa-4x valign_middle"></i> Note that online software is also available here to compute correlation matrix and to plot a correlogram without any installation.
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<div id="graph-of-correlation-matrix-using-symnum-function" class="section level1">
<h1>Graph of correlation matrix using symnum function</h1>

The R function symnum can be used to easily highlight the highly correlated variables. It replaces correlation coefficients by symbols according to the value.

The simplified format of the function is :

<pre class="r"><code>symnum(x, cutpoints = c(0.3, 0.6, 0.8, 0.9, 0.95),
symbols = c(" ", ".", ",", "+", "*", "B"))</code>[/pre]

- x is the correlation matrix to visualize
- cutpoints : correlation coefficient cutpoints. The correlation coefficients between 0 and 0.3 are replaced by a space (" “; correlation coefficients between 0.3 and 0.6 are replace by”.“; etc …
- symbols : the symbols to use.

The following R code performs a correlation analysis and displays a graph of the correlation matrix :

<pre class="r"><code>## Correlation matrix
corMat<-cor(mtcars)
head(round(corMat,2))</code>[/pre]

<code>       mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb

mpg   1.00 -0.85 -0.85 -0.78  0.68 -0.87  0.42  0.66  0.60  0.48 -0.55

cyl  -0.85  1.00  0.90  0.83 -0.70  0.78 -0.59 -0.81 -0.52 -0.49  0.53

disp -0.85  0.90  1.00  0.79 -0.71  0.89 -0.43 -0.71 -0.59 -0.56  0.39

hp   -0.78  0.83  0.79  1.00 -0.45  0.66 -0.71 -0.72 -0.24 -0.13  0.75

drat  0.68 -0.70 -0.71 -0.45  1.00 -0.71  0.09  0.44  0.71  0.70 -0.09

wt   -0.87  0.78  0.89  0.66 -0.71  1.00 -0.17 -0.55 -0.69 -0.58  0.43</code>

<pre class="r"><code>## Correlation graph for visualization
## abbr.colnames=FALSE to avoid abbreviation of column names
symnum(corMat, abbr.colnames=FALSE)</code>[/pre]

<code>     mpg cyl disp hp drat wt qsec vs am gear carb

mpg  1                                         

cyl  +   1                                     

disp +   *   1                                 

hp   ,   +   ,    1                            

drat ,   ,   ,    .  1                         

wt   +   ,   +    ,  ,    1                    

qsec .   .   .    ,          1                 

vs   ,   +   ,    ,  .    .  ,    1            

am   .   .   .       ,    ,          1         

gear .   .   .       ,    .          ,  1      

carb .   .   .    ,       .  ,    .          1 

attr(,"legend")

[1] 0 ' ' 0.3 '.' 0.6 ',' 0.8 '+' 0.9 '*' 0.95 'B' 1</code>

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<div id="conclusions" class="section level1">
<h1>Conclusions</h1>
<div class="block">
One of the easy way to visualize correlation matrix in R is to use the symnum() R function.
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<div id="infos" class="section level1">
<h1>Infos</h1>
<pre class="warning"><code>This analysis was performed using R (ver. 3.1.0).</code>[/pre]
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