importdata() cannot do this.
If you use textscan() then immediately after the format string you can give a number indicating the number of times the format string is to be used -- so you could use
textscan(fid, '%f %f', 100)
for example.
Alternately you can use techniques similar to what I did in https://www.mathworks.com/matlabcentral/answers/447889-how-do-i-read-data-from-a-dat-file-seperated-by-lines-of-text-into-individual-vectors#answer_363508 but in your case instead of matching against '^\s*#' you would match against '^[^0-9-]' which would match any line whose first character was not a digit or the character '-' (as I assume that some of your data might be negative.)
