Abstract
Periodic pattern detection is an important data mining task that highlights the temporal regularities within the data. It aims at finding if a partial or full pattern has a cyclic repetition in the considered time series or data sequence. Periodicity is found in large number of datasets including meteorological data, transaction count, computer network traffic, power consumption, sunspots, Electrocardiography (ECG), biological sequences such as DNA and protein [33]. Periodic pattern analysis not only helps in understanding the behavior of the data but also contributes in predicting the future trends of the data. There are several algorithms reported in the literature for periodicity detection in time series and biological sequences [3,34] but none of these algorithms discuss the non-uniformly sampled data. General assumption in the time series and sequence data is that the consecutive data values are sampled at regular or uniform interval of time. But this assumption hardly holds in real datasets; for example the stock market data analyzed in this paper record various features for each working day. This data has a quite a few missing values for weekly and arbitrary holidays. Although handling this issue is not very complex but requires careful handling. In this paper we analyze the stock market data in detail and show how the periodic pattern analysis may provide the understanding of the data to predict the future trends. Our experimental results show that consideration of missing values in stock market data results in much larger number of interesting results than the trivial periodicity detection approach ignoring the missing values.