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Asked: 2026-06-15T10:32:44+00:00

I wrote the following function: x <- 1:4 y <- c(1,2,7,4) mydf <- data.frame(a=x,b=x,c=x,d=x,y=y)

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I wrote the following function:

x    <- 1:4
y    <- c(1,2,7,4)
mydf <- data.frame(a=x,b=x,c=x,d=x,y=y)

practice  <-  function(x) if( x[1] == x[5]) {

             foo <- (x[2])
             return(foo)

              } else {

              bar     <- x[3] + x[4]                
              foobar <- x[2] - bar

               return(foobar)
              }       

newmydf <- apply( mydf, 1, practice)

this works fine on the data.frame provided. However I have another data.frame and I keep getting 

Error in x[3] + x[4] : non-numeric argument to binary operator

despite the following str()

'data.frame':   133 obs. of  19 variables:
 $  : chr   ...
 $ : int   ...
 $ : int  ...
 $ : int  ...
 $ : int   ...
 $ : int   ...
 $ : int   ...
 $ : int   ...
 $ : int  ...
 $ : int  ...
 $ : int   ...
 $ : int   ...
 $ : int  ...
 $ : int  ...
 $ : int   ...
 $ : int  ...
 $ : num  ...
 $ : int  
 $ : int

What possible little slip ups can I be making? I have started with a new session and I still get the same issue.

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1 Answer

  1. Editorial Team

    The values in the first column of second data frame are of type “character”. As a result, the command apply turns the whole data frame into a character matrix. The operator + is not defined for character values.

    There are two possible solutions:

    1. Transform the first column to type numeric (if possible):

      mydf[ , 1] <- as.numeric(mydf[ , 1])

    2. Do not use the first column of the data frame:

      apply(mydf[ , -1], 1, practice)
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