When working with R I frequently get the error message &quot;subscript out of bounds&quot;. [For example][1]:

    # Load necessary libraries and data
    library(igraph)
    library(NetData)
    data(kracknets, package = &quot;NetData&quot;)

    # Reduce dataset to nonzero edges
    krack_full_nonzero_edges &lt;- subset(krack_full_data_frame, (advice_tie &gt; 0 | friendship_tie &gt; 0 | reports_to_tie &gt; 0))

    # convert to graph data farme 
    krack_full &lt;- graph.data.frame(krack_full_nonzero_edges) 
 
    # Set vertex attributes
    for (i in V(krack_full)) {
        for (j in names(attributes)) {
            krack_full &lt;- set.vertex.attribute(krack_full, j, index=i, attributes[i+1,j])
        }
    }

    # Calculate reachability for each vertix
    reachability &lt;- function(g, m) {
        reach_mat = matrix(nrow = vcount(g), 
                           ncol = vcount(g))
        for (i in 1:vcount(g)) {
            reach_mat[i,] = 0
            this_node_reach &lt;- subcomponent(g, (i - 1), mode = m)
 
            for (j in 1:(length(this_node_reach))) {
                alter = this_node_reach[j] + 1
                reach_mat[i, alter] = 1
            }
        }
        return(reach_mat)
    }
 
    reach_full_in &lt;- reachability(krack_full, &#39;in&#39;)
    reach_full_in

This generates the following error `Error in reach_mat[i, alter] = 1 : subscript out of bounds`.

However, my question is not about this particular piece of code (even though it would be helpful to solve that too), but my question is more general:

* What is the definition of a subscript-out-of-bounds error? What causes it?
* Are there any generic ways of approaching this kind of error?


  [1]: http://sna.stanford.edu/sna_R_labs/lab_2.R

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Subscript out of bounds - general definition and solution?