"Apply()" Command for finding Summaries on Rows / Columns of a Matrix or Dataframe Object

 

"Apply()" Command for finding Summaries on Rows / Cols

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* The "ColMeans()" and "RowSums()" command are designed as quick alternatives to a more generalised command "Apply()"

 

* The "apply()" command enables one to apply a function to rows or columns of a matrix or a dataframe

 

* The general form of the "Apply()" command is given in the following manner :

apply(X,margin,FUN,....)

 

In this command , the applicable MARGIN within the parameter is either 1 or 2 where 1 is for the rows and 2 is for the columns applicable for the dataframe

 

* One can replace the "FUN" part within the parameter of the apply() function and one can also add additional instructions which might be appropriate to the command / function that one is applying

 

* Example :

One might add the parameter "na.rm = TRUE " as an instruction to the apply function .

> mat01

     [,1] [,2] [,3] [,4]

[1,]    1    2    3    4

[2,]    5    6    7    8

[3,]    9   10   11   12

[4,]   13   14   15   16

 

> apply (mat01 , 1 , mean , na.rm = TRUE )

[1]  2.5  6.5 10.5 14.5

 

* In such a case , one can see that the row names of the original dataframe are displayed as output .

 

* If the dataframe has no set row names , then one will see the result as a vector of values .

 

> apply (fw , 1 , median , na.rm = TRUE )

2.5  6.5 10.5 14.5