Pandas : Precision error when converting string to float

Using pandas to deal with timestamps, I am concatening two columns and then convert the result in floating. It appears that when I display the two columns I observe two different results. How can the conversion from string to float can affect the value? Thanks for your help.

Here is the content of the data.csv file

epoch_day,epoch_ns

1533081601,224423000

Here is my test program:

import pandas as pd

pd.options.display.float_format = '{:.10f}'.format

df_mid = pd.read_csv("data.csv")



df_mid['result_1']=df_mid['epoch_day'].astype(str).str.cat(df_mid['epoch_ns'].astype(str), sep =".")

df_mid['result_2'] = df_mid['epoch_day'].astype(str).str.cat(df_mid['epoch_ns'].astype(str), sep =".").astype(float)

print(df_mid)

The result is :

   epoch_day   epoch_ns              result_1              result_2

0  1533081601  224423000  1533081601.224423000 1533081601.2244229317

Thanks for your help

asked Nov 13 '18 at 5:16

fxtokyo

add a comment |

Here is the content of the data.csv file

epoch_day,epoch_ns

1533081601,224423000

Here is my test program:

import pandas as pd

pd.options.display.float_format = '{:.10f}'.format

df_mid = pd.read_csv("data.csv")



df_mid['result_1']=df_mid['epoch_day'].astype(str).str.cat(df_mid['epoch_ns'].astype(str), sep =".")

df_mid['result_2'] = df_mid['epoch_day'].astype(str).str.cat(df_mid['epoch_ns'].astype(str), sep =".").astype(float)

print(df_mid)

The result is :

   epoch_day   epoch_ns              result_1              result_2

0  1533081601  224423000  1533081601.224423000 1533081601.2244229317

Thanks for your help

asked Nov 13 '18 at 5:16

fxtokyo

add a comment |

Here is the content of the data.csv file

epoch_day,epoch_ns

1533081601,224423000

Here is my test program:

import pandas as pd

pd.options.display.float_format = '{:.10f}'.format

df_mid = pd.read_csv("data.csv")



df_mid['result_1']=df_mid['epoch_day'].astype(str).str.cat(df_mid['epoch_ns'].astype(str), sep =".")

df_mid['result_2'] = df_mid['epoch_day'].astype(str).str.cat(df_mid['epoch_ns'].astype(str), sep =".").astype(float)

print(df_mid)

The result is :

   epoch_day   epoch_ns              result_1              result_2

0  1533081601  224423000  1533081601.224423000 1533081601.2244229317

Thanks for your help

asked Nov 13 '18 at 5:16

fxtokyo

Here is the content of the data.csv file

epoch_day,epoch_ns

1533081601,224423000

Here is my test program:

import pandas as pd

pd.options.display.float_format = '{:.10f}'.format

df_mid = pd.read_csv("data.csv")



df_mid['result_1']=df_mid['epoch_day'].astype(str).str.cat(df_mid['epoch_ns'].astype(str), sep =".")

df_mid['result_2'] = df_mid['epoch_day'].astype(str).str.cat(df_mid['epoch_ns'].astype(str), sep =".").astype(float)

print(df_mid)

The result is :

   epoch_day   epoch_ns              result_1              result_2

0  1533081601  224423000  1533081601.224423000 1533081601.2244229317

Thanks for your help

string pandas precision floating-accuracy

asked Nov 13 '18 at 5:16

fxtokyo

asked Nov 13 '18 at 5:16

fxtokyo

asked Nov 13 '18 at 5:16

fxtokyo

asked Nov 13 '18 at 5:16

fxtokyo

asked Nov 13 '18 at 5:16

fxtokyo

add a comment |

1 Answer
1

active

oldest

votes

Floating-point numbers are represented in computer hardware as base 2 (binary) fractions. Most decimal fractions cannot be represented exactly as binary fractions.

When you convert your string, python creates a float which is the closest binary fraction for your input.

You can actually see to which decimal number this corresponds by running the following:

from decimal import Decimal

Decimal(1533081601.224423000)

OUTPUT: Decimal('1533081601.224422931671142578125')

You can see the Python documentation for more info https://docs.python.org/2/tutorial/floatingpoint.html

answered Nov 20 '18 at 17:40

Guilherme Costa

515

Thanks a lot for your explanation @guilherm-costa.
– fxtokyo
Nov 28 '18 at 2:02

Thanks for the feedback. Could you please accept the answer?
– Guilherme Costa
Nov 28 '18 at 12:31

add a comment |

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1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

Floating-point numbers are represented in computer hardware as base 2 (binary) fractions. Most decimal fractions cannot be represented exactly as binary fractions.

When you convert your string, python creates a float which is the closest binary fraction for your input.

You can actually see to which decimal number this corresponds by running the following:

from decimal import Decimal

Decimal(1533081601.224423000)

OUTPUT: Decimal('1533081601.224422931671142578125')

You can see the Python documentation for more info https://docs.python.org/2/tutorial/floatingpoint.html

answered Nov 20 '18 at 17:40

Guilherme Costa

515

Thanks a lot for your explanation @guilherm-costa.
– fxtokyo
Nov 28 '18 at 2:02

Thanks for the feedback. Could you please accept the answer?
– Guilherme Costa
Nov 28 '18 at 12:31

add a comment |

Floating-point numbers are represented in computer hardware as base 2 (binary) fractions. Most decimal fractions cannot be represented exactly as binary fractions.

When you convert your string, python creates a float which is the closest binary fraction for your input.

You can actually see to which decimal number this corresponds by running the following:

from decimal import Decimal

Decimal(1533081601.224423000)

OUTPUT: Decimal('1533081601.224422931671142578125')

You can see the Python documentation for more info https://docs.python.org/2/tutorial/floatingpoint.html

answered Nov 20 '18 at 17:40

Guilherme Costa

515

Thanks a lot for your explanation @guilherm-costa.
– fxtokyo
Nov 28 '18 at 2:02

Thanks for the feedback. Could you please accept the answer?
– Guilherme Costa
Nov 28 '18 at 12:31

add a comment |

Floating-point numbers are represented in computer hardware as base 2 (binary) fractions. Most decimal fractions cannot be represented exactly as binary fractions.

When you convert your string, python creates a float which is the closest binary fraction for your input.

You can actually see to which decimal number this corresponds by running the following:

from decimal import Decimal

Decimal(1533081601.224423000)

OUTPUT: Decimal('1533081601.224422931671142578125')

You can see the Python documentation for more info https://docs.python.org/2/tutorial/floatingpoint.html

answered Nov 20 '18 at 17:40

Guilherme Costa

515

Floating-point numbers are represented in computer hardware as base 2 (binary) fractions. Most decimal fractions cannot be represented exactly as binary fractions.

When you convert your string, python creates a float which is the closest binary fraction for your input.

You can actually see to which decimal number this corresponds by running the following:

from decimal import Decimal

Decimal(1533081601.224423000)

OUTPUT: Decimal('1533081601.224422931671142578125')

You can see the Python documentation for more info https://docs.python.org/2/tutorial/floatingpoint.html

answered Nov 20 '18 at 17:40

Guilherme Costa

515

answered Nov 20 '18 at 17:40

Guilherme Costa

515

answered Nov 20 '18 at 17:40

Guilherme Costa

515

answered Nov 20 '18 at 17:40

Guilherme Costa

515

Thanks a lot for your explanation @guilherm-costa.
– fxtokyo
Nov 28 '18 at 2:02

Thanks for the feedback. Could you please accept the answer?
– Guilherme Costa
Nov 28 '18 at 12:31

add a comment |

Thanks a lot for your explanation @guilherm-costa.
– fxtokyo
Nov 28 '18 at 2:02

Thanks for the feedback. Could you please accept the answer?
– Guilherme Costa
Nov 28 '18 at 12:31

Thanks a lot for your explanation @guilherm-costa.
– fxtokyo
Nov 28 '18 at 2:02

Thanks for the feedback. Could you please accept the answer?
– Guilherme Costa
Nov 28 '18 at 12:31

add a comment |

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