Creating a tdm with only one variable - r

Question

So I need to prepare a term-document-matrix for each of the sets of text I want to subsequently run against each other in a classification procedure (rolling.classify() in Stylo package).
So I created a tdm of the whole text corpus, then want to make two sets only of selected texts, one which should contain one text only. So multiple texts works fine (a), but one texts only does not (b), I cannot do this?
freq.list <- make.frequency.list(words, head = 265) # Creating frequency list using only the frequencies of the
# selected features from word-list (words)
word.frequencies <- make.table.of.frequencies(corpus = x, features = freq.list)
# Document-term matrix of whole corpus and matching frequencies.
# Making two subsets now:
a <- word.frequencies[c(1,2,3,17,19,20,21,22,23), 1:263]
dim(a) # Double-check that it is the right no. of texts
b <- word.frequencies[18,1:263]
dim(b) # Double-check
> dim(a)
[1] 9 263
> dim(b)
NULL
data:
(used dput())
x <- structure(list(middleFr_Calmative_1946 = c("the", "calmative",
"i", "don’t", "know", "when", "i", "died", ".", "it", "always",
"seemed", "to", "me", "i", "died", "old", ",", "about", "ninety",
"years", "old", ",", "and", "what", "years", ",", "and", "that",
"my", "body", "bore", "it", "out", ",", "from", "head", "to",
"foot", ".", "but", "this", "evening", ",", "alone", "in", "my",
"icy", "bed", ",", "i", "have", "the", "feeling", "i’ll", "be",
"older", "than", "the", "day", ",", "the", "night", ",", "when",
"the", "sky", "with", "all", "its", "lights", "fell", "upon",
"me", ",", "the", "same", "i", "had", "so", "often", "gazed",
"resolved", "to", "speak", "to", "him", ".", "so", "i", "marshalled",
"the", "words", "and", "opened", "my", "mouth", ",", "thinking",
"i", "would", "hear", "them", ".", "but", "all", "i", "heard",
"was", "a", "kind", "of", "rattle", ",", "unintelligible", "even",
"have", "a", "penny", "in", "my", "pocket", ",", "nor", "anything",
"resembling", "it", "."), middleFr_End_1946 = c("the", "end",
"they", "clothed", "me", "and", "gave", "me", "money", ".", "i",
"back", "mine", ".", "i", "added", ",", "give", "me", "back",
"my", "greatcoat", ".", "they", "replied", "that", "they", "had",
"burnt", "them", ",", "together", "with", "my", "other", "clothes",
".", "i", "understood", "then", "that", "the", "end", "was",
"near", ",", "at", "least", "fairly", "near", ".", "later", "on",
"i", "tried", "to", "exchange", "this", "hat", "for", "a", "cap",
",", "or", "a", "slouch", "which", "could", "be", "pulled", "down",
"over", "my", "face", ",", "but", "without", "much", "success",
".", "and", "yet", "i", "could", "not", "go", "about", "bare",
"-", "headed", ",", "with", "my", "skull", "in", "the", "state",
"it", "was", ".", "at", "first", "this", "hat", "was", "too",
"small", ",", "then", "it", "got", "used", "to", "me", ".", "they",
"gave", "me", "a", "tie", ",", "after", "long", "discussion",
".", "it", "seemed", "a", "pretty", "tie", "to", "me", ",", "but",
"i", "didn’t", "like", "it", ".", "when", "it", "came", "at",
"last", "i", "was", "too", "tired", "to", "send", "it", "back",
".", "but", "in", "the", "end", "it", "came", "in", "useful",
".", "it", "was", "blue", ",", "with", "kinds", "of", "little",
"stars", ".", "i", "didn’t", "feel", "well", ",", "but", "they",
"told", "me", "i", "was", "well", "enough", "."), middleFr_Expelled_1946 = c("the",
"expelled", "there", "were", "not", "many", "steps", ".", "i",
"had", "counted", "them", "a", "thousand", "times", ",", "both",
"going", "up", "and", "coming", "down", ",", "but", "the", "figure",
"has", "gone", "from", "my", "mind", ".", "i", "have", "never",
"known", "whether", "you", "should", "say", "one", "with", "your",
"every", "day", "several", "times", "a", "day", ",", "until",
"they", "sink", "forever", "in", "the", "mud", ".", "that’s",
"an", "order", ".")), class = "stylo.corpus", call = load.corpus.and.parse(files = "all",
corpus.dir = "x", markup.type = "plain", corpus.lang = "English.all",
splitting.rule = ("[ \t\n]+"), sampling = "no.sampling",
features = "w", ngram.size = 1, preserve.case = FALSE, encoding = "UTF-8"))
freq.list <- c("", "-", "—", ",", ";", ":", "!", "?", ".", "’", "\"",
"(", ")", "a", "about", "above", "across", "after", "again",
"against", "ah", "all", "almost", "along", "Already", "also",
"always", "am", "among", "an", "and", "another", "any", "anything",
"are", "as", "at", "away", "back", "be", "because", "been", "before",
"behind", "being", "best", "better", "between", "beyond", "both",
"but", "by", "came", "can", "can't", "can’t", "cannot", "come",
"comes", "could", "did", "didn’t", "different", "do", "does",
"doing", "don't", "don’t", "done", "down", "each", "either",
"else", "even", "ever", "every", "everything", "except", "far",
"few", "fifteen", "first", "five", "for", "forward", "four",
"from", "get", "go", "goes", "going", "got", "great", "had",
"half", "has", "have", "having", "he", "her", "here", "herself",
"him", "himself", "his", "how", "however", "hundred", "i", "i'll",
"i'm", "i’ll", "if", "in", "indeed", "instead", "into", "is",
"it", "it's", "it’s", "its", "itself", "just", "last", "late",
"least", "left", "less", "let", "like", "little", "long", "made",
"make", "many", "may", "me", "merely", "might", "mine", "more",
"most", "moved", "much", "must", "my", "myself", "near", "neither",
"never", "next", "no", "none", "nor", "not", "nothing", "now",
"of", "off", "often", "oh", "on", "once", "one", "only", "or",
"other", "others", "otherwise", "our", "out", "over", "own",
"perhaps", "place", "quite", "rather", "really", "right", "said",
"same", "say", "second", "shall", "she", "should", "since", "six",
"small", "so", "some", "someone", "something", "sometimes", "somewhere",
"soon", "still", "such", "ten", "than", "that", "that's", "that’s",
"the", "their", "them", "themselves", "then", "there", "therefore",
"these", "they", "thing", "things", "third", "this", "those",
"though", "three", "through", "thus", "till", "time", "times",
"to", "together", "too", "towards", "two", "under", "unless",
"until", "up", "upon", "us", "very", "was", "way", "we", "well",
"went", "were", "what", "whatever", "when", "where", "whether",
"which", "while", "who", "whom", "whose", "why", "will", "with",
"within", "without", "won't", "would", "yes", "yet", "you", "your",
"yourself")

Answer 1

You can do:
b <- word.frequencies[18,1:263, drop = F]
dim(b)
# [1] 1 263