I am currently reading the book "Introduction to statistical learning" and on Page 3 there is a problem statement regarding the SMarket data (stock exchange data) fig 2.2 whose left panel states the relation shown is the percentage vs up/down trend of stock market. But here Author is saying that one box for 648 days and one for 602 days.

I don't quite get that. There is no information given for the days. Is the print faulty or am I missing something here? If someone has gone through the book and has any idea, please help me to understand the following chart.

picture of the book page in question

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    $\begingroup$ perhaps he means the number of data points represented in each box plot? $\endgroup$ – tintinthong Aug 28 '17 at 5:15

The left-handed panel of Figure 1.2 displays two boxplots of the previous day's percentage changes in the stock index: one for the 648 days for with the market increased on subsequent days, and one for the 602 days for which the market decreased.

The blue boxplot of the left-most figure is based on data from 648 days. These days are not randomly chosen, they are selected because they have a special characteristic: the day after the market increased. The red boxblot in the left-most figure is based on 602 days for which the market decreased the day after.

In short, the red and blue boxplot visualize multiple datapoints.

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