null output of "explain" function from "fastshap" package

[shamimashrafiyan]

I have a Random Forest model and a data frame dataset. I am using this command to find the SHAP for the training dataset:

SHAP1 <- fastshap::explain(my_model, X = train_dataset, pred_wrapper = predict, nsim = 1)

It works when I run it on a data frame (2 dimensions) but I would like to get SHAP just for one sample so my dataset changes to a vector. when I run the above code for one sample(one row), the output is "A tibble: 1 × 0" or " a data frame with 1 row and 0 columns".
So is there a way to get SHAP of a sample? Does "explain" work for a sample?

Thanks in advance

[technocrat]

I'm unclear about "one sample." Do you mean a data frame acting as a test_dataset. The X argument has to contain all the variables used to construct my_model; it can't just be train_dataset[1] (subsetting a single column to create a vector) or train_dataset[1:10,] (taking a subset of the rows of a data frame) because, all other things being equal a portion of the rows of the data set used to construct the model has less information than the total.

[shamimashrafiyan]

@technocrat
Ok let me be clear by giving an example:
I have a dataset named A (15*80) so "A" has 15 samples or rows and it has 79 features and the last column is 'target'.
I train a model on training dataset for example A[ 1: 60, 1:79], and I already have my model which named "my_model"
So I wanna find SHAP for one sample(one row), let s say first sample. So I should write this command:

SHAP1 <- fastshap::explain(my_model, X = A[1,1: ncol(A) - 1],  pred_wrapper = predict, nsim = 1)

So look at X which is A[1, 1: ncol(A) - 1] which shows the first row of "A" and all features or columns of "A", but 'target' (last column).
Actually X is: A[1, 1:79]
Is it clear now?

my question is: If I give the training sample to the X, it works perfectly, even it works for 2, 3, 4 and more but for one sample(one row) it doesn't work.