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Data Analysis Preparing Data for Analysis Data Cleaning Cleaning A CSV Part 2

Posted by kawa
kawa
5,856 Points

Filling out missing values

At about minute 3 missing values of "Golbat" (row 42 of dataframe "data") are filled out. My question is how it is possible that a new object/row is created (golbat = data.loc[42]), values in it changed and then the values of the data frame (data) change correspondig? Aren't these to seperate objects? Which Python rule applies here? Thank you for your help!

golbat = data.loc[42]
golbat["Height (in)"] = 63
golbat["Weight (lbs)"] = 121.30

data.loc[42]

2 Answers

Mel Rumsey
.a{fill-rule:evenodd;}techdegree seal-36
Mel Rumsey
Treehouse Moderator

Hey there kawa ! By creating golbat = data.loc[42] we are creating a reference to that specific row. When we change the values of weight and height for the referenced value, the values change in the dataframe.

kawa
kawa
5,856 Points

Hello Mel, thank you for you answer! Is this a specialty of the pandas.loc() function? If the same principle applies, a should have the value of 2 aswell in the below example. Which it doesn't. 

1. a = 1
2. b = 0
3. b = a 
4. b  = b + 1
# b=2 and a remains 1
Michael Young
Michael Young
6,267 Points
Michael Young
Michael Young
6,267 Points

I'm using pandas version 2.2.3. Entering and executing:

golbat = data.loc[42]
golbat["Height (in)"] = 63
golbat["Weight (lbs)"] = 121.30

returns "SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame" and points to this documentation

Revising the code like this:

data.loc[42, "Height (in)"] = 63
data.loc[42, "Weight (lbs)"] = 121.30
data.loc[68, "Type"] = "Fighting"
data.loc[87, "Type"] = "Water"

successfully edits the columns with missing values as evident by data[data.isnull().any(axis=1)] returning no hits.