rloopsfunction-calls

How to Iterate over a column in a data frame to change its values

I have a data frame that looks like:

ID     A     B    
 0     8    25  
 1    16   123  
 2     4   120  
...             ...

What I want to do now is to iterate over column 'A' for example and call a function with the value of the cell and return it at the same location.

For example a function like (x^2)-1. 

int calculation(int val){
   return val*val-1;
}

...code...

while(i<A.length){
  A[i] = calculation(A[i]);
}

So the result should look like this. 

ID     A     B    
 0    63    25  
 1   265   123  
 2    15   120  
...             ...



I am new to R, if you know some good basic guidelines or books for scientific plotting, let me know. :-)

Thanks for your help.

Solution

  • This is very straightforward task in R.

    a<-c(8,16,4)
b<-c(25,123,120)
df<-data.frame(a,b)

calculation<-function(a){
  a^2-1
}


# Method 1
df$a<-(df$a^2)-1

# Method 2
df$a<-calculation(df$a)