pandas数据样本行列选取

注：以下代码是基于python3.5.0编写的

import pandas

food_info = pandas.read_csv("food_info.csv")
# ------------------选取数据样本的第一行--------------------
print(food_info.loc[0])

#------------------选取数据样本的3到6行----------------------
print(food_info.loc[3:6])

#------------------head选取数据样本的前几行------------------
print(food_info.head(2))

# ------------------选取数据样本的2,5,10行,两种方法-----------
# print(food_info.loc[[2,5,10]])         #方法一 
two_five_ten = [2,5,10]                  #方法二
print(food_info.loc[two_five_ten])

# ------------------选取数据样本的NDB_No列--------------------
# ndb_col = food_info["NDB_No"]          #方法一  
col_name = "NDB_No"                      #方法二
ndb_col = food_info[col_name]
print(ndb_col)

# ------------------选取数据样本的多列-------------------
# zinc_copper = food_info[["Zinc_(mg)", "Copper_(mg)"]]
columns = ["Zinc_(mg)", "Copper_(mg)"]
zinc_copper = food_info[columns]
print(zinc_copper)

# ---------------------综合小例子----------------------------
col_names = food_info.columns.tolist()     #把所有的行转化成list
print(col_names)
gram_columns = []

for c in col_names:                        #遍历col_names，找出所有以(g)结尾的位置
    if c.endswith("(g)"):
        gram_columns.append(c)
print(gram_columns)
gram_df = food_info[gram_columns]          #把所有以(g)结尾的列存放到gram_df
print(gram_df.head(3))                     #打印前3行