Python for Data Science: Loop
While loop
while condition :
expression
# loop while the condition is true
For loop
# basic for loop
for a in list:
expression
# access to index
for index, a in enumerate(list):
expression
# stings
Looping data structures
dict, numpy array, pandas
Dictionary
for key, value in dict.items():
print(key + "--" + str(value))
Numpy array
for a in my_array:
print(a)
# for 1D numpy array elements will be printed out one by one
# for 2D numpy array arrays will be printed out one by one
for a in np.nditer(my_array):
print(a)
# elements will be printed out one by one
# notice that np.nditer() is a function, while dict.items is a method
Pandas
- By default
import pandas as pd
my_data = pd.read_csv("my_data", index_col = 0)
for a in my_data:
print(a)
# column names will be printed out.
- iterrows
for label,row in my_data.iterrows():
print(label)
print(row)
# selective print, use row[index], or loc, iloc
- add column
# for example for lab, row in my_data.iterrows()： my_data[lab, "new_column"] = my_data["column1"].upper() - apply
# for example cars['COUNTRY'] = cars['country'].apply(str.upper) cars['COUNTRY'] = cars['country'].apply(len)
Reference
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