Error generated

This gives the error shown.

```
library(qeML)
set.seed(123)
ix <- sample(10, 15, replace = TRUE) + seq(1, 150, 10) - 1
iris.ix <- iris[ix, 1:4]
qeKNN(iris.ix, "Petal.Length", k = 1)
## Error in `[.data.frame`(tst, , ycol) : undefined columns selected
```

Note that this works without error:

```
library(qeML)
set.seed(123)
qeKNN(iris[1:4], "Petal.Length", k = 1)
# ...snip...
```

and this too:

```
library(FNN)
set.seed(123)
ix <- sample(10, 15, replace = TRUE) + seq(1, 150, 10) - 1
iris.ix <- iris[ix, 1:4]
knn.reg(iris.ix[-4], y = iris.ix[[4]], k = 1)
## PRESS = 0.44
## R2-Predict = 0.9511979
```

Start by running the provided qeKNN reproduction with the sampled iris.ix data, then inspect the qeKNN entry point and compare its column handling with the working qeKNN and FNN examples. Done means the reported data shape no longer raises undefined columns selected and the existing working example remains valid.

Written by the indexing model from the issue text.