[R] what would break a citation network? [Error in as.igraph.vs(graph, vids) : Invalid vertex names]

[Drake Gossi]

Hello everyone,

I'm trying to learn how to put together a citation network, and, in
doing so, I'm playing around with a data set of my own making. I'm
going back and forth between two .csv files. One has two columns and
is simply labeled "to" and "from":

to from
rickert heidegger
rickert nietzsche
rickert parmenides
rickert diogenes
rickert latour
rickert haraway
rickert barad
rickert burke
boyle mackenzie
boyle flusser
boyle kittler
boyle massumi
boyle mattern
boyle rickert
boyle berlant
boyle ulmer
boyle manovich
boyle burke

So, rickert and boyle are academics, and the people to the right are
other scholars they cite. This one .csv file goes on for 75 rows like
this.

But I have another file too, which looks like this. The two columns
are "author" and "association":

author association
latour STS
burke rhetoric
kittler media theory
heidegger philosophy
barthes philosophy
mackenzie media theory
massumi affect theory
nietzsche philosophy
flusser media theory
rickert rhetoric
spinuzzi tech comm
boyle rhetoric
gries rhetoric
jeff rice rhetoric
jenny rice rhetoric
gunn rhetoric
rivers rhetoric
mol STS
stengers STS
barad STS
braidotti posthumanism
wolfe posthumanism
haraway STS

The trouble is, when I add the following (davis, rhetoric) onto the
second list, the citation network breaks.

...
...
braidotti posthumanism
wolfe posthumanism
haraway STS
davis rhetoric

My question is: why would the addition of a single row break the
analysis? I am getting this error message:

Error in as.igraph.vs(graph, vids) : Invalid vertex names

My code is this:

install.packages("igraph")
library(igraph)
myEdgeList <- as.matrix(read.csv("myEdgeList.csv", as.is=TRUE))
G <- graph.edgelist(myEdgeList, directed=FALSE)
myThemes <- read.csv("myThemes.csv", as.is=TRUE)
rowNumberofMatchingCases <- which(myThemes$association %in% c("rhetoric"
                                                              ))
authorsOfMatchingCases <- myThemes$author [rowNumberofMatchingCases]
H <- induced.subgraph (G, authorsOfMatchingCases)
lout <- layout.fruchterman.reingold(H)
plot.igraph(H, layout=lout, vertex.size=5, vertex.label.cex=.5)

My guess is I have broken some fundamental rule of graphing, like one
of the names performs too many functions in the graph, or I have
"rhetoric" too many times in the is the second csv file...

But I really think the better question is: if you were just fooling
around and trying to make a citation network from hand and by scratch,
like I'm doing, what could you not do with the list? and does this
have something to do with transitivity?

Drake