Slide 106 causes "undefined columns selected" error

[JayC]

On slide 106, the clust_data_NBA call shown in the slide causes an error.

the first error is easy to fix because the slide uses “STLPG” rather than “STPG”. However, once that is corrected, the command still refuses to run, and I’ve no idea why. I’ve gone over the column names multiple times but still can’t get past this step.

My code:
clust.data.NBA <- NBA[, c(“MGP”, “FG_PC”, “X3P_PC”, “FT_PC”,
“APG”, “PPG”, “STPG”, “BLKPG”)]

the error:
Error in [.data.frame(NBA, , c(“MGP”, “FG_PC”, “3P_PC”, “FT_PC”, “APG”, :
undefined columns selected

NBA.csv has an APG column and this code is basically identical to the slide.

[Merav Yuravlivker]

Hi JayC,

Thanks for your comment! Usually this error “undefined columns selected” means that your code is trying to access a column that doesn’t exist. It looks like your code has a column “X3P_PC”, and the error message has a column name “3P_PC”. I recommend to recheck your column names, as it may be that there is a typo in one of them. You can always use the code “colnames(NBA)” to see a list of all the column names in the console and then copy and paste the names into your code.

There are some other ways to subset the columns, such as identifying the column numbers instead of names or using the subset function. You can always test those out to see if they work.

Let me know if that helps!

Best,
Merav

[JayC]

The colnames command produces:
> colnames(NBA)
[1] “NAME” “TEAM” “SALARY.M.” “GP” “MPG”
[6] “PPG” “FG_PC” “X3P_PC” “FT_PC” “RPG”
[11] “APG” “STPG” “BLKPG” “POSITION”

Note that the file NBA.csv has a column titled “3P_PC”, and R doesn’t allow columns to start with a number (so it adds the “X”). This was covered in the data viz course I believe.

My point is that the code on your slide does not work and I do not understand why.

[Merav Yuravlivker]

Hi JayC,

I just ran the code

NBA = read.csv(“NBA.csv”)
clust_data_NBA = NBA[, c(“MPG”, “PPG”, “FG_PC”, “X3P_PC”,
“FT_PC”, “RPG”, “APG”, “STPG”, “BLKPG”)]

I also ran the slide from the code (as copied below):

clust_data_NBA = NBA[, c(“MPG”, “FG_PC”, “X3P_PC”, “FT_PC”,
“APG”, “PPG”, “STPG”, “BLKPG”)]

Both of these variations worked when I ran them. I recommend restarting R and RStudio, as this tends to solve problems like this, where the code does not seem to be working correctly.

Let me know if that worked!

Best,
Merav

[JayC]

So the restart didn’t work, and neither did the copy/paste of your code into my code.

But I basically rebuilt the entire expression one variable at a time and for some mysterious reason it worked.

Weird are the ways of R.

[JayC]

Also, for some reason my code is spitting out that the best number of clusters is 3, not 2.

[Merav Yuravlivker]

Hi JayC,

You are correct in that R can work in some weird ways! And for the NBA data set, I believe that we state the best number of clusters in 3, although we go over what kmeans looks like with only 2 centers to illustrate the differences.

Let me know if you have any other questions!

Best,
Merav

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