3.3 Anchor points

• the result of a (complex) query is a list of token sequences of variable length ( $\Rightarrow$ matches)
• each match is represented by two anchor points:
  match (corpus position of first token) and matchend (corpus position of last token)
• set additional target anchor with @ marker in query (prepended to a pattern)

  > "in" @[pos="DT"] [lemma="case"];
  $\to$ shown in bold font in KWIC display

• only a single token can be marked as target; if multiple @ markers are used (or if the marker is in the scope of a repetition operator such a +), only the rightmost matching token will be marked

  > [pos="DT"] (@[pos="JJ.*"] ","?){2,} [pos="NNS?"];

• when targeted pattern is optional, check how many matches have target anchor set

  > A = [pos="DT"] @[pos="JJ"]? [pos="NNS?"];
> size A;
> size A target;

• anchor points allow a flexible specification of sort keys with the general form

  > sort by attribute on start point .. end point ;

  both start point and end point are specified as an anchor, plus an optional offset in square brackets; for instance, match[-1] refers to the token before the start of the match, matchend to the last token of the match, matchend[1] to the first token after the match, and target[-2] to a position two tokens left from the target anchor

  NB: the target anchor should only be used in the sort key when it is always defined

• example: sort noun phrases by adjectives between determiner and noun

  > [pos="DT"] [pos="JJ"]{2,} [pos="NNS?"];
> sort by word %cd on match[1] .. matchend[-1];

• if end point refers to a corpus position before start point, the tokens in the sort keys are compared from right to left; e.g. sort on the left context of the match (by token)

  > sort by word %cd on match[-1] .. match[-42];

  whereas the reverse option sorts on the left context by character

  > sort by word %cd on match[-42] .. match[-1] reverse;

• complex sort operations can sometimes be speeded up by using an external helper program (the standard Unix sort tool)⁴

  > sort by word %cd;
> set ExternalSort on;
> sort by word %cd;
> set ExternalSort off;

• the count command accepts the same specification for the strings to be counted

  > count by lemma on match[1] .. matchend[-1];

• display corpus positions of all anchor points in tabular format

  > A = "behind" @[pos="JJ"]? [pos="NNS?"];
> dump A;
> dump A 9 14;$\quad$ (10 $^{\text{th}}$ - 15 $^{\text{th}}$ match)

  the four columns correspond to the match, matchend, target and keyword (see Section 3.6) anchors; a value of -1 means that the anchor has not been set:

          1019887 1019888 -1      -1
          1924977 1924979 1924978 -1
          1986623 1986624 -1      -1
          2086708 2086710 2086709 -1
          2087618 2087619 -1      -1
          2122565 2122566 -1      -1
  

  note that a previous sort or count command affects the ordering of the rows (so that the $n$-th row corresponds to the $n$-th line in a KWIC display obtained with cat)

• the output of a dump command can be written (>) or appended (>>) to a file, if the first character of the filename is |, the ouput is sent to the pipe consisiting of the following command(s); use the following trick to display the distribution of match lengths in the query result A:

  > A = [pos="DT"] [pos="JJ.*"]* [pos="NNS?"];
> dump A > "| gawk '{print $2 - $1 + 1}' | sort -nr | uniq -c | less";

• see Section 6.4 for an opposite to the dump command, which may be useful for certain tasks such as locating a specific corpus position