[R] loop testing unidentified columns

[Brittany Demmitt]

Thank you!

> On Jun 20, 2016, at 12:41 PM, David L Carlson <dcarlson at tamu.edu> wrote:
> 
> It does not test the first column, but a vector must have consecutive indices. Since you did not assign a value, R inserts a missing value. If you don't want to see it use
> 
>> results.pc.all[, -1]
>          [,1] [,2]
> results.2    1    2
> results.3    2    3
> 
> -------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77840-4352
> 
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Brittany Demmitt
> Sent: Monday, June 20, 2016 12:15 PM
> To: r-help at r-project.org
> Subject: [R] loop testing unidentified columns
> 
> Hello,
> 
> I want to compare all of the columns of one data frame to another to see if any of the columns are equivalent to one another. The first column in both of my data frames are the sample IDs and do not need to be compared. Below is an example of the loop I am using to compare the two data frames that counts the number of equivalent values there between two columns. So in this example the value of 3 means that all three observations for the two columns being compared were equivalent. The loop works fine but I do not understand why it tests the first column of the sample IDs providing “NA” for the sum of matching when my loop is specifying to only test columns 2-3.  
> 
> Thank you!
> 
> 
> #create dataframe A 
> A = matrix(c("a",3,4,"b",5,7,"c",3,7),nrow=3, ncol=3,byrow = TRUE)    
> A <- as.data.frame(A)
> A$V2 <- as.numeric(A$V2)
> A$V3 <- as.numeric(A$V3)
> str(A)
> 
> #create dataframe B
> B = matrix(c("a",1,1,"b",6,2,"c",2,2),nrow=3, ncol=3,byrow = TRUE)    
> B <- as.data.frame(B)
> B$V2 <- as.numeric(B$V2)
> B$V3 <- as.numeric(B$V3)
> str(B)
> 
> results.2 <- numeric()
> results.3  <- numeric()
> 
> 
> #compare columns to identify those that are identical in the two dataframes 
> for(i in 2:3){
>  results.2[i] <- sum(A[,2]==B[,i])
>  results.3[i] <- sum(A[,3]==B[,i])
>  results.pc.all <- rbind(results.2,results.3)
> }
> results.pc.all
> 
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