Find Maximum Values by year in timeseries dataframe, keeping the date

df2=df1.ix[df1.groupby(df1.index.year).idxmax().iloc[:,0]]

Find common timespan/ years in multiple time series/ dataframes

#concatenate vertically all dataframes
dfAlldf=pd.concat([df1, df2,df3,df4], axis=1)     

#sort them by the date (datetimeindex)

dfAlldf=dfAlldf.sort_index()    

#group dataframe by years

grps=dfAlldf.groupby(dfAlldf.index.year)           

#empty dataframe for populating with complete years

dfCompl=pd.DataFrame()

# for each group of years                                

for g in grps:

    #if don't have any null values in year, in any column 

    if not any(g[1].isnull().any(axis=1)):           

        #concatenate in dfCompl

        dfCompl=pd.concat([dfCompl, g[1]], axis=0)     

# re-sort by index

dfCompl=dfCompl.sort_index()                      

Pandas - Reading headers and dates correctly from Clipboard/ CSV

When using pandas funcions read_clipboard() or read_csv() you have to define if your data has headers (column headers) and indexes (row headers).

If you're passing indexes with datetime format, make sure if it will be parsed correctly, indicating it's a datetime and if it has dayfirst format (dd/mm/YYYY).

For example:

pd.read_clipboard(index_col=0, headers=None,parse_dates=True, dayfirst=True)

Is telling pandas that the table in clipboard has no column headers, but have index (row headers) in the first column and it is in datetime format with day first (dd/mm/YYYY).

Logarithmic and Exponential Curve Fit in Python - Numpy

With numpy function "polyfit":

X,y : data to be fitted

import numpy as np

1. Exponential fit

cf = np.polyfit(X, np.log(y), 1)

will return two coefficients, who will compose the equation:

exp(cf[1])*exp(cf[0]*X)


2. Logarithm fit:

cf = np.polyfit(np.log(X), y, 1)

will return two coefficients, who will compose the equation:

cf[0]*log(X)+cf[1]

Interpolate missing values in pandas DataFrame

If we have a dataframe with dates and flows - with missing values, as example below:

        0
2019-01-31 50.208308
2019-02-28 50.623457
2019-03-31 56.203933
2019-04-30 NaN
2019-05-31 NaN
2019-06-30 117.727655
2019-07-31 62.273259
2019-08-31 49.054898
2019-09-30 55.612575
2019-10-31 54.187409

We can use the function pandas interpolate, and interpolate the data with different methods

dfIn.interpolate() - will fill noData with linear interpolation;
dfIn.interpolate(method='polynomial', order=3) - will fill noData with 3rd degree polinomial interpolation;

Result:
                linear  polinomial    original
2019-01-31   50.208308   50.208308   50.208308
2019-02-28   50.623457   50.623457   50.623457
2019-03-31   56.203933   56.203933   56.203933
2019-04-30   76.711840   89.513986         NaN
2019-05-31   97.219748  124.233259         NaN
2019-06-30  117.727655  117.727655  117.727655
2019-07-31   62.273259   62.273259   62.273259
2019-08-31   49.054898   49.054898   49.054898
2019-09-30   55.612575   55.612575   55.612575
2019-10-31   54.187409   54.187409   54.187409

Pandas - Select only numeric columns

df=df.select_dtypes(include=['float64'])

will return only the float values of the 'df' dataframe.

Excel to Python Pandas DataFrame

The most easy way is to use the clipboard. Just copy your table in Excel to the clipboard, and then call the read_clipboard method from pandas:

df1 = pd.read_clipboard()

Pandas can read Excel files directly too, with read_excel

df1 = pd.read_excel('tmp.xlsx',index_col=0, header=0)

Taking care with header and indexes, and other options as described here.

Maximum, minimum and average monthly precipitation

Below is shown some panda commands for retrieving maximum, minimum and average monthly precipitation from daily precipitation data.

The daily precipitation is assumed to be in a pandas DataFrame, with its index in Datetime index format.

1 - Daily to monthly precipitation
df_m=df1.resample('M').sum()

2 - Maximum monthly precipitation
p_max=df_m.groupby(df_m.index.month).max()

3 - Minimum monthly precipitation
p_min=df_m.groupby(df_m.index.month).min()

4 - Average monthly precipitation
p_avg=df_m.groupby(df_m.index.month).mean()

How to extract all numbers / floats from a string with python regex

import re

stringWithNumbers='anystring2with 6.89 numbers3.55 3.141312'
digits = re.findall("[-+]?\d+\.?\d*", stringWithNumbers)

Fitting IDF curves with Scipy and Pandas

# -*- coding: utf-8 -*-
"""
Created on Tue Jul 10 11:19:37 2018

@author: rodrigo.goncalves
"""
import pandas as pd
from scipy.optimize import minimize
 
# This is the IDF function, returning the sum of squared errors (SSE)
def func2(par, res):
    p1 =  (par[0] * res.index.values  **par[1])
    p2 = ((res.columns.values.astype(float)+par[2])**par[3])
    f = pd.DataFrame([p/p2 for p in p1],index=res.index,columns=res.columns)
    erroTotQ=((f-res)**2).sum(axis=1).sum()    
    return erroTotQ
 
# copy your rainfall intensities table from excel
# with column headers with rainfall durations
# and row names with Return period value in years
dfInt=pd.read_clipboard()

#initial guess
param1 = [5000, 0.1, 10, 0.9]

res2 = minimize(func2, param1, args=(dfInt,), method='Nelder-Mead')
print(res2)
cs=['K=','a=','b=','c=']
dfResult=pd.DataFrame(res2.x,index=cs).transpose()
print(dfResult)
dfResult.to_clipboard(index=None)