# Import NumPy, Pandas, SciPy, Matplotlib, Datetime
import numpy as np
import pandas as pd
from scipy import stats, interpolate
import matplotlib.pyplot as plt
import matplotlib.dates as mdates
from datetime import datetime, timedelta

# Give Colab access to Google Drive
from google.colab import drive
drive.mount('/content/drive')

# Load CSV file using Pandas with 2 different settings
global_temp = pd.read_csv(filepath,index_col='Year')                          # loaded years as integer numbers
global_temp_dt = pd.read_csv(filepath,index_col='Year',parse_dates=['Year'])  # loaded years as Datetime objects

# Display CSV file
display(global_temp)
display(global_temp_dt)

# 1. Make a black line plot of the 1980-2019 time series.
#    Add scatter points for each year.
#    Add a grid and axis labels.
plt.figure(figsize=(13,6))
plt.plot(global_temp.index,global_temp['Temp_anomaly'],c='k',label='Original data')
plt.scatter(global_temp.index,global_temp['Temp_anomaly'],c='k')
plt.grid()
plt.xlabel('Years')
plt.ylabel('Temperature anomaly (°C)')

# 2. Use SciPy's linregress() to calculate a linear regression on the entire 1880-2019 time series.
#    For this, use the variable "global_temp" (where the years are integer numbers).
#    This should be just one line of code.
slope, intercept, rvalue, pvalue, stderr = stats.linregress(global_temp.index,global_temp['Temp_anomaly'])
# or you can send some outputs to a "throwaway" underscore:
slope, _, rvalue, pvalue, _ = stats.linregress(global_temp.index,global_temp['Temp_anomaly'])

# 3. Print the slope (including units), r-squared value, and p-value.
#    Round each to 3 decimal places.
print('The slope from 1880-2019 is:',round(slope,3),'°C/year (using the integer year version)')
print('The r^2 value is:',round(rvalue**2,3))
print('The p-value is:',round(pvalue,3))

# 4. Repeat Part #1, but use the variable "global_temp_dt" (where the years are Datetime objects).
#    Remember you have to convert the Datetime array of years to numbers.
slope_days, _, _, _, _ = stats.linregress(mdates.date2num(global_temp_dt.index),global_temp_dt['Temp_anomaly'])

# 5. Print the slope from the regression in Part #3, using units of °C/year.
print('The slope from 1880-2019 is:',round(365.25*slope_days,3),'°C/year (using the Datetime version)')

# 6. In these Python comment lines, answer the following questions:
#    a. How much variance in the data is explained by the regression?
#           A: ~75%
#    b. Is the 1880-2019 trend significant at the 95% confidence level?
#           A: Yes, because it's basically zero, which is less than 0.05
#    c. Is a linear regression appropriate for this data?
#           A: Probably not - data looks more like a quadratic curve

# 7. If you have time, on your plot from earlier, draw the regression line that you just calculated.
#    Make it a red dashed line.
#    Label it and add a legend.
x_values = global_temp.index
y_values = slope * x_values + intercept
plt.plot(x_values,y_values,'r--',lw=3,label='1880-2019 linear regression')
plt.legend()

# 1. Make a black line plot of the 1980-2019 time series.
#    Add scatter points for each year.
#    Add a grid and axis labels.
plt.figure(figsize=(13,6))
plt.plot(global_temp.index,global_temp['Temp_anomaly'],c='k',label='Original data')
plt.scatter(global_temp.index,global_temp['Temp_anomaly'],c='k')
plt.grid()
plt.xlabel('Years')
plt.ylabel('Temperature anomaly (°C)')

# 2. Create two new variables:
#    - Select years 1880-1969 of the "global_temp" data set and save the data as "gt_old".
#    - Select years 1970-2019 of the "global_temp" data set and save the data as "gt_new".
gt_old = global_temp.loc[1880:1969]
gt_new = global_temp.loc[1970:2019]

# 3. Use SciPy's linregress() to calculate two separate linear regressions on the two time series "gt_old" and "gt_new".
#    Give the output variables slightly different names (e.g. "slope_old" and "slope_new").
slope_old, intercept_old, rvalue_old, _, _ = stats.linregress(gt_old.index,gt_old['Temp_anomaly'])
slope_new, intercept_new, rvalue_new, _, _ = stats.linregress(gt_new.index,gt_new['Temp_anomaly'])

# 4. Print the slope (including units) and r-squared values for each time segment (1880-1969, 1970-2019).
#    Round each to 3 decimal places.
print('The slope from 1880-1969 is:',round(slope_old,3),'°C/year')
print('The r^2 value for 1980-1969 is:',round(rvalue_old**2,3))
print('The slope from 1970-2019 is:',round(slope_new,3),'°C/year')
print('The r^2 value for 1970-2019 is:',round(rvalue_new**2,3))

# 5. In these Python comment lines, answer the following questions:
#    a. What conclusion would you draw by comparing the slopes from 1880-1969 and 1970-2019?
#           A: Warming has accelerated
#    b. What conclusion would you draw by comparing the r^2 values from 1880-1969 and 1970-2019?
#           A: Temperature variability is more fully explained by the second regression
#    c. Would a linear regression on the full data (from 1880-2019) be appropriate?
#           A: No, the data might be approximately piecewise linear, but not fully linear

# 6. If you have time, on your plot from earlier, draw the two regression lines that you just calculated.
#    Make one a blue dotted line and the other a blue dashed line.
#    Label them and add a legend.
x_values_old = gt_old.index
y_values_old = slope_old * x_values_old + intercept_old
plt.plot(x_values_old,y_values_old,'b:',lw=3,label='1880-1969 linear regression')
x_values_new = gt_new.index
y_values_new = slope_new * x_values_new + intercept_new
plt.plot(x_values_new,y_values_new,'b--',lw=3,label='1970-2019 linear regression')
plt.plot(x_values,y_values,'r--',lw=3,label='1880-2019 linear regression')
plt.legend()

# 1. Create a copy of "global_temp" and save it as a new variable, "gt_missing_1990s".
gt_missing_1990s = global_temp.copy()

# 2. Run the following lines of code to delete years 1990-1999 from "gt_missing_1990s".
years_missing_1990s = range(1990,2000)
gt_missing_1990s = gt_missing_1990s.drop(years_missing_1990s)

# 3. Use SciPy's interp1d() to linearly interpolate the data in "gt_missing_1990s"
#    to the missing years, which are stored in the variable "years_missing_1990s".
interp_func = interpolate.interp1d(gt_missing_1990s.index,gt_missing_1990s['Temp_anomaly'],
                                   kind='linear',bounds_error=False,fill_value=np.NaN)
gt_new_1990s = interp_func(years_missing_1990s)

# 4. Make a black solid line plot of the original 1880-2019 time series in "global_temp".
#    Add a grid and axis labels.
plt.figure(figsize=(13,6))
plt.plot(global_temp.index,global_temp['Temp_anomaly'],c='k',label='Original data')
plt.grid()
plt.xlabel('Years')
plt.ylabel('Temperature anomaly (°C)')

# 5. On the same plot, add red scatter points for the incomplete time series in "gt_missing_1990s".
plt.scatter(gt_missing_1990s.index,gt_missing_1990s['Temp_anomaly'],c='r',label='Incomplete data')

# 6. On the same plot, add blue scatter points for the temperatures interpolated to years in "years_missing_1990s".
plt.scatter(years_missing_1990s,gt_new_1990s,c='b',label='Interpolated data')

# 7. Add label arguments to your plot functions above, then add a legend.
plt.legend();

# 8. In these Python comment lines, answer the following questions:
#    a. How would you rate the accuracy of the interpolated temperature estimates for 1990-1999?
#           A: Decent, since they pass through the original (real) data
#    b. How would the interpolation look different if data were missing from 1990-2001 instead of 1990-1999?
#           A: Very different; this shows how sensitive interpolation is to start/end values

# 1. Create a copy of "global_temp" and save it as a new variable, "gt_missing_ww2".
gt_missing_ww2 = global_temp.copy()

# 2. Run the following lines of code to delete years 1935-1945 from "gt_missing_ww2".
years_missing_ww2 = range(1935,1946)
gt_missing_ww2 = gt_missing_ww2.drop(years_missing_ww2)

# 3. Use SciPy's interp1d() to linearly interpolate the data in "gt_missing_ww2"
#    to the missing years, which are stored in the variable "years_missing_ww2".
interp_func = interpolate.interp1d(gt_missing_ww2.index,gt_missing_ww2['Temp_anomaly'],
                                   kind='linear',bounds_error=False,fill_value=np.NaN)
gt_new_ww2 = interp_func(years_missing_ww2)

# 4. Make a black solid line plot of the original 1880-2019 time series in "global_temp".
#    Add a grid and axis labels.
plt.figure(figsize=(13,6))
plt.plot(global_temp.index,global_temp['Temp_anomaly'],c='k',label='Original data')
plt.grid()
plt.xlabel('Years')
plt.ylabel('Temperature anomaly (°C)')

# 5. On the same plot, add red scatter points for the incomplete time series in "gt_missing_ww2".
plt.scatter(gt_missing_ww2.index,gt_missing_ww2['Temp_anomaly'],c='r',label='Incomplete data')

# 6. On the same plot, add blue scatter points for the temperatures interpolated to years in "years_missing_ww2".
plt.scatter(years_missing_ww2,gt_new_ww2,c='b',label='Interpolated data')

# 7. Add label arguments to your plot functions above, then add a legend.
plt.legend();

# 8. In these Python comment lines, answer the following questions:
#    a. How would you rate the accuracy of the interpolated temperature estimates for 1935-1945?
#         A: Quite poor; the interpolated points miss the temporary bump in temperature
#    b. What does this experience tell you about linear interpolation?
#         A: Linear interpolation is only good when the data are behaving linearly, 
#            and the start, middle, and end values are not outliers