下标超出范围-一般定义和解决方案? [英] Subscript out of bounds - general definition and solution?

问题描述

使用R时，我经常收到错误消息下标超出范围". 例如:

When working with R I frequently get the error message "subscript out of bounds". For example:

# Load necessary libraries and data
library(igraph)
library(NetData)
data(kracknets, package = "NetData")

# Reduce dataset to nonzero edges
krack_full_nonzero_edges <- subset(krack_full_data_frame, (advice_tie > 0 | friendship_tie > 0 | reports_to_tie > 0))

# convert to graph data farme 
krack_full <- graph.data.frame(krack_full_nonzero_edges) 

# Set vertex attributes
for (i in V(krack_full)) {
    for (j in names(attributes)) {
        krack_full <- set.vertex.attribute(krack_full, j, index=i, attributes[i+1,j])
    }
}

# Calculate reachability for each vertix
reachability <- 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 <- 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 <- reachability(krack_full, 'in')
reach_full_in

这会产生以下错误Error in reach_mat[i, alter] = 1 : subscript out of bounds.

但是，我的问题不是关于这段特定的代码(尽管也可以解决该问题)，但是我的问题更笼统:

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:

• 下标越界错误的定义是什么?是什么原因造成的?
• 有没有通用的方法来处理这种错误?

推荐答案

这是因为您尝试访问超出其边界的数组.

This is because you try to access an array out of its boundary.

我将向您展示如何调试此类错误.

I will show you how you can debug such errors.

1. 我设置了options(error=recover)

2. 我运行reach_full_in <- reachability(krack_full, 'in') 我得到了:

1. I set options(error=recover)

2. I run reach_full_in <- reachability(krack_full, 'in') I get :

reach_full_in <- reachability(krack_full, 'in')
Error in reach_mat[i, alter] = 1 : subscript out of bounds
Enter a frame number, or 0 to exit   
1: reachability(krack_full, "in")

我输入1并得到

I enter 1 and I get

 Called from: top level 

我键入ls()来查看我当前的变量

I type ls() to see my current variables

  1] "*tmp*"           "alter"           "g"               
     "i"               "j"                     "m"              
    "reach_mat"       "this_node_reach"

现在，我将看到变量的尺寸:

Now, I will see the dimensions of my variables :

Browse[1]> i
[1] 1
Browse[1]> j
[1] 21
Browse[1]> alter
[1] 22
Browse[1]> dim(reach_mat)
[1] 21 21

您会看到alter已超出范围. 22> 21.在该行中:

You see that alter is out of bounds. 22 > 21 . in the line :

  reach_mat[i, alter] = 1

为避免此类错误，我个人是这样做的:

To avoid such error, personally I do this :

• 尝试使用applyxx功能.它们比for
更安全
• 我使用seq_along而不是1:n(1:0)
• 如果可以避免使用mat[i,j]索引访问，请尝试考虑矢量化解决方案.

• Try to use applyxx function. They are safer than for
• I use seq_along and not 1:n (1:0)
• Try to think in a vectorized solution if you can to avoid mat[i,j] index access.

EDIT矢量化解决方案

例如，在这里我看到您没有使用set.vertex.attribute是矢量化的事实.

For example, here I see that you don't use the fact that set.vertex.attribute is vectorized.

您可以替换:

# Set vertex attributes
for (i in V(krack_full)) {
    for (j in names(attributes)) {
        krack_full <- set.vertex.attribute(krack_full, j, index=i, attributes[i+1,j])
    }
}

由此:

##  set.vertex.attribute is vectorized!
##  no need to loop over vertex!
for (attr in names(attributes))
      krack_full <<- set.vertex.attribute(krack_full, 
                                             attr, value = attributes[,attr])

这篇关于下标超出范围-一般定义和解决方案?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！