This function calculates the H-index of input vertices and works with both directed and undirected networks.

`h_index(graph, vertices = V(graph), mode = "all")`

- graph
A graph (network) of the igraph class.

- vertices
A vector of desired vertices, which could be obtained by the V function.

- mode
The mode of H-index depending on the directedness of the graph. If the graph is undirected, the mode "all" should be specified. Otherwise, for the calculation of H-index based on incoming connections select "in" and for the outgoing connections select "out". Also, if all of the connections are desired, specify the "all" mode. Default mode is set to "all".

A vector including the H-index of each vertex inputted.

Other centrality functions:
`betweenness()`

,
`clusterRank()`

,
`collective.influence()`

,
`degree()`

,
`lh_index()`

,
`neighborhood.connectivity()`

,
`sirir()`

```
if (FALSE) {
MyData <- coexpression.data
My_graph <- graph_from_data_frame(MyData)
GraphVertices <- V(My_graph)
h.index <- h_index(graph = My_graph, vertices = GraphVertices, mode = "all")
}
```