Odtnhj

I am trying to read the whitespace separated values, apply Savitzky-Golay filter to one of the columns, round the column to 6 decimal digits, plot the graph and export the data to the new file. Here is the working code where I commented out the line which makes graph window 'Not responding':

import pandas as pd
from datetime import datetime
import numpy as np
import matplotlib.pyplot as plt
from scipy.signal import savgol_filter

df = pd.read_csv('data.txt', delim_whitespace = True)

plt.plot(df.index, df.rotram, '-', lw=4)
#plt.plot(df.index, savgol_filter(df.rotram, 21, 3), 'r-', lw=2)

# smooth the 'rotram' column using Savitzky-Golay filter
df.rotram = savgol_filter(df.rotram, 21, 3)

# round to 6 decimal digits
#df.rotram = df.rotram.map(':.6f'.format) # <-- not responding when plotting
#df["rotram"] = df["rotram"].map(':,.6f'.format) # the same as above (not responding when plotting)

# When plot is removed then above rounding works well
plt.plot(df.index, df.rotram, 'r-', lw=2)

df.to_csv('filtered.txt', sep='t')

plt.show()

print "End"

The sample data looks like:

otklon rotram lakat rotnad
-6.240000 -3.317000 -34.445000 16.805000 
-6.633000 -3.501000 -34.519000 17.192000 
-5.099000 -2.742000 -34.456000 15.059000 
-6.148000 -3.396000 -34.281000 17.277000 
-4.797000 -3.032000 -34.851000 16.052000 
-5.446000 -2.964000 -34.459000 15.677000 
-6.341000 -3.490000 -34.934000 17.300000 
-6.508000 -3.465000 -35.030000 16.722000 
-6.513000 -3.505000 -35.018000 16.845000 
-6.455000 -3.501000 -35.302000 16.896000
.
.
.
(more than 20000 lines)

The separator in the input file is space + TAB + space.

If I uncomment the line df.rotram = df.rotram.map(':.6f'.format) then program hangs (Not responding) with the empty graph although saved data is correct.

If I then remove the line plt.plot(df.index, df.rotram, 'r-', lw=2) then the program ends normally.

Although saving the data to file after rounding works well, plotting doesn't :-/

If you want to round your column to the Nth decimal place, use pd.Series.round or np.around:

df.rotram = df.rotram.round(decimals=6)
# Or,
# df.rotram = np.around(df.rotram, decimals=6)

However, I would still like to know why the above code doesn't work as
expected.

When you call map, you convert your numeric column to a string. Pandas will plot this data without making any assumptions. For your sample data, the plot looks hideous:

Versus, the latter case using round:

The plots are completely different (in the former case, each string is sorted lexicographically and given its own tick on the y-axis).