Issues converting rounded float to string pandas

Question

I'm rounding a column from my dataframe to the nearest 5 floating point. After that I'm converting the column values into string, but when I do that the float go back as if they were unrounded. I'm using Python 2.7

import pandas as pd
df=pd.read_excel(C:"path")

def custom_round(x, base=5):
    return base * round(float(x)/base)

df['A'] = df['kl'].apply(lambda x: custom_round(x, base=.05))
df['b'] = "D = "  + df['A'].astype(str)


     kl     A                       b  
 0.600001  0.60  D = 0.6000000000000001  
 0.600001  0.60  D = 0.6000000000000001  
 0.600000  0.60  D = 0.6000000000000001  
 0.600000  0.60  D = 0.6000000000000001  
 0.600587  0.60  D = 0.6000000000000001  
 0.601573  0.60  D = 0.6000000000000001  
 0.601168  0.60  D = 0.6000000000000001  
 0.600001  0.60  D = 0.6000000000000001  
 0.600001  0.60  D = 0.6000000000000001  
 0.600001  0.60  D = 0.6000000000000001  
 0.600000  0.60  D = 0.6000000000000001  
 0.600001  0.60  D = 0.6000000000000001  
 0.600001  0.60  D = 0.6000000000000001  
 0.600001  0.60  D = 0.6000000000000001  
 0.600001  0.60  D = 0.6000000000000001  
 0.850001  0.85  D = 0.8500000000000001

score 2 · Accepted Answer · answered Jun 29 '18 at 15:07

Here I think you can use string formatting. I use '${:,.2f}'.format(1234.5) (source here) for formatting dollars and cents, but I was able to use the same formatting method in a lambda function for your float to string.

import pandas as pd 
data = {'kl' : [0.600001, 0.600001, 0.600000, 0.600000, 
                0.600587, 0.601573, 0.601168, 0.600001, 
                0.600001, 0.600001, 0.600000, 0.600001, 
                0.600001, 0.600001, 0.600001, 0.850001]}
df = pd.DataFrame.from_dict(data)

def custom_round(x, base=5):
    return base * round(float(x)/base)

df['A'] = df['kl'].apply(lambda x: custom_round(x, base=.05))
df['b'] = "D = " + df['A'].apply(lambda s: '{:,.5f}'.format(s))

This answer is good just change your number inside `{:,.2f}'.format(s)` to 2 — Jose Vasquez, Jun 29 '18 at 15:29
@JoseVasquez Your initial question says you are rounding to the nearest 5 floating point, which I thought was the 5th decimal place. If this answer is not what you requested, please let me know and I will update it accordingly. — BenG, Jun 29 '18 at 15:51

kosnik · Answer 2 · 2018-06-29T15:19:40.777

0

First do the rounding using your function

df['A'] = df['kl'].apply(lambda x: custom_round(x, base=.05))

Now, you can use python's string formatting to round your floats

df['b'] =  df['A'].apply(lambda x:  'D = ' + '{:.5f}'.format(x))

I am not sure if this is valid for python 2.7, if not you can try

df['b'] = df['A'].apply(lambda x:  'D = ' + '%.5f' % (x,))

edited Jun 29 '18 at 15:19

answered Jun 29 '18 at 14:55

kosnik

2,342
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This doesn't work when I said 5th nearest it is not the 5th decimal place. E.g `0.4323 = 0.45, 0.49 = 0.50, 0.7124 = 0.70.` – Jose Vasquez Jun 29 '18 at 15:12
then just apply the rounding before formatting the string. I will update my answer to cover that – kosnik Jun 29 '18 at 15:18

Issues converting rounded float to string pandas

2 Answers2