the"[]" at the end of terms indicates that no tags have been assigned. If a term, say "house" would have the POS tag NN (for noun singular) assigned the term call would look like "house [NN (POS)]". If the term has not tags assigned the brackets are empty and the term cell looks like "house []". These brackets are part of the term information but not part of the term text. To see the actual word in that term you can use the Term to String node that extracts the word(s) as strings and removed the assigned tags.
The problem is I see this [] alone in some rows with no associed terms.
This single -alone [] have a tif value so I think all datas are wrong.
In fact it will be good if this alone [] (with no associed words) will not be present in the bag of words.
In my workflow, I use :
Document data extractor > case converter > replacer (for french punctuation stripping) > table creator + dictionary tager + tag filter (for stop words exclusion in french) > Bag of words > TF
In the TF output table I see :
Row ID
Term
Document
TF rel
1
révolution[]
Document x
0.044
2
[]
Document x
0.044
3
française[]
Document x
0.044
<p>This [] is a problem because the TF of the document not really correct.</p>
<p>Thanks for your help,</p>
<p> </p>
<p>David</p>
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as Geo mentioned you can use the N Chars Filter node to filter out words existing of only a few (n) chars. Use the filter before countnig the TF values.