## Interpolation for Missing Values

Have you ever worked with data that has gaps or missing values? Perhaps you’re dealing with a time series of stock prices and some of the days are missing.

In such cases, interpolation can be used to estimate the missing values. Interpolation refers to the process of estimating missing values by using the values that are available.

There are different methods of interpolation, such as linear interpolation, polynomial interpolation, and interpolation through padding. In this article, we will discuss these methods of interpolation in detail.

## Using Interpolation for Missing Values in Series Data

One of the most common applications of interpolation is in time-series data. A time series is a sequence of data points recorded over time.

Examples include daily stock prices, daily temperature readings, or the number of website visitors per day. In such datasets, some values may be missing for a variety of reasons.

Perhaps the equipment used to collect the data failed or was being upgraded, or there was a data entry mistake. One method of estimating missing values in a series is through linear interpolation.

Linear interpolation is a simple method that involves using a straight line to connect two known points and then using this line to estimate the missing value. Suppose we have a time series of daily temperatures and some of the values are missing.

To use linear interpolation to estimate the missing values, we would simply draw a straight line between the two known values on either side of the missing value. Another method of estimating missing values in a series is polynomial interpolation.

Polynomial interpolation is more complex than linear interpolation and involves fitting a polynomial curve to the known data points and using this curve to estimate the missing value. Polynomial interpolation is useful when the relationship between the data points is not linear but can be approximated by a curve.

### Interpolation through Padding

Another method of interpolating missing values is through padding. Padding involves filling in the missing values with a value that is a function of the neighboring values.

For example, we could fill in missing values with the median, mean, or mode of the neighboring values. Padding is a simple but effective method of interpolation, especially for datasets with small gaps.

### Limitations of Interpolation

It is important to note that interpolation is only an estimation and should be used with caution. Estimated values may not be entirely accurate, and the error may increase with the distance between the known points.

Interpolation assumes that the data is smooth and that the missing value is close to the known values. If the data is not smooth or has sudden spikes or dips, interpolation may not be appropriate.

Additionally, interpolation methods assume that the data is evenly spaced, either in time or in some other dimension. If the data is unevenly spaced, other methods of interpolation may be required.

### Interpolation in Pandas DataFrames

Pandas is a popular Python library used for data manipulation and analysis. Pandas helps you to work with tabular data, including time series data.

It offers several methods of interpolation for dealing with missing values.

### Linear Interpolation with Pandas Dataframe

To use linear interpolation with a pandas dataframe, we can use the “interpolate” function. The default interpolation method is linear, but other methods are available.

For example, we can use cubic interpolation or quadratic interpolation.

### Interpolation through Padding with Pandas Dataframe

To use padding interpolation with a pandas dataframe, we can use the “fillna” function. We can fill the missing values with the mean, median, mode, or any other value.

## Conclusion

Interpolation is a powerful method of estimating missing values in datasets. It can be used with different types of data, including time series data.

Linear interpolation and polynomial interpolation are useful for estimating missing values in a series, while padding interpolation is useful for smaller gaps. Pandas offer convenient methods of using interpolation with dataframes, making it easy to deal with missing values in a tabular dataset.

However, it is important to use the appropriate interpolation method for the data and to be aware of the limitations of interpolation. In the previous sections of this article, we discussed interpolation and its applications for dealing with missing values in data. We looked at different methods of interpolation such as linear interpolation, polynomial interpolation, and interpolation through padding.

We also discussed how pandas data frame can be utilized for interpolation purposes. In this section, we will delve deeper into some of the topics and examine them in detail.

### Linear Interpolation:

Linear interpolation is a simple method of interpolation that draws a straight line between the two known data points and estimates the missing value by following this line. It is a common method of interpolation and is widely used across different domains, such as finance, engineering, and environmental sciences.

The advantage of linear interpolation is that it is simple to implement and does not require any specialized knowledge of statistical techniques. However, when the data is highly irregular or the curve deviates from linearity, linear interpolation may not deliver accurate results.

Moreover, the estimation may be affected by outliers, skewness, and other issues. Polynomial Interpolation:

### Polynomial Interpolation:

Polynomial interpolation is a more advanced form of interpolation that fits a polynomial function to the available data points and utilizes this function for prediction purposes.

Unlike linear interpolation, polynomial interpolation is better suited for non-linear data sets and is more accurate in predicting values that lie between the data points. However, the downside of polynomial interpolation is that it can give rise to oscillations that are not present in the original data.

Moreover, extrapolation using a polynomial function can lead to unexpected results and should be used with caution.

### Interpolation through Padding:

Interpolation through padding is another method of estimating missing values. This method assumes that the missing value can be replaced by a value derived from the surrounding data points.

Padding can be either backward-oriented or forward-oriented. Backward padding fills the missing value with the value preceding it, while forward padding fills the missing value with the value that comes after it.

Padding carries the advantage of simplicity and is easier to implement than other forms of interpolation. Nonetheless, padding suffers from a disadvantage in that it cannot detect sudden changes in the data and is better suited for small gaps rather than long stretches of incomplete data.

### Pandas Data Frame Interpolation:

Pandas is a powerful Python library that helps in data manipulation and analysis. It offers several built-in functions for interpolation, such as “interpolate” and “fillna”.

With Pandas, you can use these built-in functions to fill missing values by adopting different interpolation methods. One of the advantages of using Pandas for interpolation is the intuitive interface it provides, which makes it easy to work with tabular data.

Additionally, Pandas has affordable computation costs, making it practical for handling large datasets. Pandas also has excellent documentation and a large user community, which means that support is available whenever it is needed.

### Limitations of Interpolation:

Although interpolation is useful in estimating missing values, it should be used with caution. Interpolation methods assume that the data is equally spaced, which might not always be the case.

Moreover, the accuracy of estimation decreases with the size of the gap between known data points. When dealing with irregular data or data that has sudden changes, interpolation may not always be a feasible solution.

Finally, it is important to verify the accuracy of the estimation by comparing the estimates with actual data points.

## Conclusion:

Missing values are a common problem in data analysis, which can affect the quality of insights drawn from the data. Interpolation offers a solution that can be used to estimate missing values by utilizing the surrounding data points.

The method of interpolation used should be chosen based on the nature of the data and the accuracy required. Pandas offers a convenient interface for handling missing values, and the built-in functions help in implementing interpolation without specialized knowledge of statistics.

However, caution should be taken when using interpolation as the accuracy of the estimation can be affected by the nature of the data. Finally, it is important to re-iterate that interpolation is only an estimation method and the accuracy of the results should be verified against the original data.

In conclusion, Interpolation is a powerful tool that offers solutions for dealing with missing values in data. This article has explored different methods of interpolation, such as linear interpolation, polynomial interpolation, and interpolation through padding, and examined their applications in pandas data frame.

While these methods offer various advantages for estimating missing values, it is important to consider the limitations of each technique and use them carefully. The takeaways from this article are that interpolation should be used based on the nature of the data, interpolation is only an estimation, and the accuracy of the results should be verified against the original data.

Interpolation is a practical solution that can be used to improve the quality of insights drawn from data, and Pandas offer an intuitive interface for handling missing values.