笔记

Data and Variables

　　Data are pieces of information about individuals organized into variables. By an individual, we mean a particular person or object. By a variable, we mean a particular characteristic of the individual.

While，a dataset is a set of data identified with particular circumstances.

　　（i.e.数据是个体组织成变量的信息集合。个体可以是物体。变量是个体的特征）

　　Variables can be classified into one of two types: categorical or quantitative.

　　Categorical variables take category or label values and place an individual into one of several groups. Each observation can be placed in only one category, and the categories are mutually exclusive.

　　Quantitative variables take numerical values and represent some kind of measurement.

　　(i.e.一个跟数字有关，一个跟数字无关。而且类别变量是相互独立的，而数字变量则不是。）