1. A method of reducing a number of encoding words in data compression, comprising the steps of: converting repeated data in signal sequence based upon a length between two of the repeated data, a number of the repeated data and a kind of the repeated data to generate converted data, a portion of the converted data having an activation sequence number k being referenced by t k ; selecting a predetermined signal a; predicting a Group B that contains elements each representing the activation sequence number k for a portion of the converted data t k that contains none of the predetermined signal a, the portion of the converted data also having an inversely converted value that is equal to that of the predetermined signal a, the portion of the converted data being defined as a marking signal; comparing the position k of all of the converted data except for a portion containing the predetermined signal A to the elements in the Group B to generate a comparison result; and assigning a predetermined encoding word to the corresponding portion the converted data t k based upon the comparison result.