既然要得到的是频率玫瑰图，就要求出每个方向上在这个月中出现的次数，然后除上整个月的风向次数。通过对比，发现利用极坐标比直角坐标更简便些，故利用 find（）寻找方向值，length计算方向的长度，polar绘制玫瑰图(Since you want a frequency rose diagram, ask for the number of times per month in each direction, and then count the number of winds in the whole month. By contrast, it is found that it is easier to use polar coordinates than rectangular coordinates. Therefore, find () is used to find the direction value, length to calculate the length of the direction, and polar to draw the rose diagram)