# Kaggle: House Prices: Advanced Regression Techniques - Trying to fill in missing values

I've been playing around with the data in Kaggle's House Prices: Advanced Regression Techniques and while replicating Poonam Ligade's exploratory analysis I wanted to see if I could create a model to fill in some of the missing values.

Poonam wrote the following code to identify which columns in the dataset had the most missing values:

```
import pandas as pd
train = pd.read_csv('train.csv')
null_columns=train.columns[train.isnull().any()]
>>> print(train[null_columns].isnull().sum())
LotFrontage 259
Alley 1369
MasVnrType 8
MasVnrArea 8
BsmtQual 37
BsmtCond 37
BsmtExposure 38
BsmtFinType1 37
BsmtFinType2 38
Electrical 1
FireplaceQu 690
GarageType 81
GarageYrBlt 81
GarageFinish 81
GarageQual 81
GarageCond 81
PoolQC 1453
Fence 1179
MiscFeature 1406
dtype: int64
```

The one that I'm most interested in is LotFrontage, which describes 'Linear feet of street connected to property'. There are a few other columns related to lots so I thought I might be able to use them to fill in the missing LotFrontage values.

We can write the following code to find a selection of the rows missing a LotFrontage value:

```
cols = [col for col in train.columns if col.startswith("Lot")]
missing_frontage = train[cols][train["LotFrontage"].isnull()]
>>> print(missing_frontage.head())
LotFrontage LotArea LotShape LotConfig
7 NaN 10382 IR1 Corner
12 NaN 12968 IR2 Inside
14 NaN 10920 IR1 Corner
16 NaN 11241 IR1 CulDSac
24 NaN 8246 IR1 Inside
```

I want to use scikit-learn's linear regression model which only works with numeric values so we need to convert our categorical variables into numeric equivalents. We can use pandas get_dummies function for this.

Let's try it out on the LotShape column:

```
sub_train = train[train.LotFrontage.notnull()]
dummies = pd.get_dummies(sub_train[cols].LotShape)
>>> print(dummies.head())
IR1 IR2 IR3 Reg
0 0 0 0 1
1 0 0 0 1
2 1 0 0 0
3 1 0 0 0
4 1 0 0 0
```

Cool, that looks good. We can do the same with LotConfig and then we need to add these new columns onto the original DataFrame. We can use pandas concat function to do this.

```
import numpy as np
data = pd.concat([
sub_train[cols],
pd.get_dummies(sub_train[cols].LotShape),
pd.get_dummies(sub_train[cols].LotConfig)
], axis=1).select_dtypes(include=[np.number])
>>> print(data.head())
LotFrontage LotArea IR1 IR2 IR3 Reg Corner CulDSac FR2 FR3 Inside
0 65.0 8450 0 0 0 1 0 0 0 0 1
1 80.0 9600 0 0 0 1 0 0 1 0 0
2 68.0 11250 1 0 0 0 0 0 0 0 1
3 60.0 9550 1 0 0 0 1 0 0 0 0
4 84.0 14260 1 0 0 0 0 0 1 0 0
```

We can now split data into train and test sets and create a model.

```
from sklearn import linear_model
from sklearn.model_selection import train_test_split
X = data.drop(["LotFrontage"], axis=1)
y = data.LotFrontage
X_train, X_test, y_train, y_test = train_test_split(X, y, random_state=42, test_size=.33)
lr = linear_model.LinearRegression()
model = lr.fit(X_train, y_train)
```

Now it's time to give it a try on the test set:

```
>>> print("R^2 is: \n", model.score(X_test, y_test))
R^2 is:
-0.84137438493
```

Hmm that didn't work too well - an R^2 score of less than 0 suggests that we'd be better off just predicting the average LotFrontage regardless of any of the other features. We can confirm that with the following code:

```
from sklearn.metrics import r2_score
>>> print(r2_score(y_test, np.repeat(y_test.mean(), len(y_test))))
0.0
```

whereas if we had all of the values correct we'd get a score of 1:

```
>>> print(r2_score(y_test, y_test))
1.0
```

In summary, not a very successful experiment. Poonam derives a value for LotFrontage based on the square root of LotArea so perhaps that's the best we can do here.