8 Ways to Clean Data Using Data Cleaning Techniques

by | Aug 14, 2018 | Data Science

13 Min Read. |

Data forms the backbone of any data analytics you do. Regarding data, there are many things to go wrong – be it the construction, arrangement, formatting, spellings, duplication, extra spaces, and so on. To perform the data analytics properly we need various data cleaning techniques so that our data is ready for analysis. It’s commonly said that,

“Data scientists spend 80% of their time cleaning and manipulating data and only 20% of their time actually analyzing it.”

Thus, it is important to grow accustomed to the process of data cleaning techniques and all of the data cleansing tools that are related to data cleansing methods. This post provides a very basic introduction to data cleansing techniques in Excel.

This post covers the following data cleaning steps in Excel along with data cleansing examples:

  1. Get Rid of Extra Spaces
  2. Select and Treat All Blank Cells
  3. Convert Numbers Stored as Text into Numbers
  4. Remove Duplicates
  5. Highlight Errors
  6. Change Text to Lower/Upper/Proper Case
  7. Spell Check
  8. Delete all Formatting

What is Data Cleaning?

Data cleansing or data cleaning is the process of identifying and removing (or correcting) inaccurate records from a dataset, table, or database and refers to recognising unfinished, unreliable, inaccurate or non-relevant parts of the data and then restoring, remodelling, or removing the dirty or crude data.

Data cleaning techniques may be performed as batch processing through scripting or interactively with data cleansing tools.

After cleaning, a dataset should be uniform with other related datasets in the operation. The discrepancies identified or eliminated may have been basically caused by user entry mistakes, by corruption in storage or transmission, or by various data dictionary descriptions of similar items in various stores.

Are Data Cleaning Techniques Essential?

Data cleaning techniques are not only an essential part of the data science process – it’s also the most time-consuming part. As the New York Times reported in a 2014 article called “For Big-Data Scientists, ‘Janitor Work’ Is Key Hurdle to Insights”,

“Data scientists … spend from 50 per cent to 80 per cent of their time mired in this more mundane labour of collecting and preparing unruly digital data, before it can be explored for useful nuggets.”

Unfortunately, Data Cleaning techniques are generally not spoken about in the media nor is it taught in most intro Data Scientist Course because it is not as important as training a neural network or identifying images but to perform those things data cleaning plays a very important role.

Without the data cleaning techniques, the neural networks and image identification modules will not be as efficient as we want them to be.

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With the rise of big data, data cleaning methods has become more important than ever before. Every industry – banking, healthcare, retail, hospitality, education – is now navigating in a large ocean of data.

And as the data pool is getting bigger, the variables of things going wrong too are getting larger. Each fault becomes difficult to find when you can’t just look at the whole dataset in a spreadsheet on your computer. In fact, this could be true for a variety of reasons.

Data Cleansing Examples and Data Cleaning Methods in Excel

In this post, I will show you various ways to clean data in Excel with data cleansing examples & data cleansing techniques.

1. Data Cleaning Techniques-Get Rid of Extra Spaces

Here I have the text Welcome To Digital Vidya written in four different ways.

welcome to digital vidya
welcome   to digital vidya
welcome     to  digital  vidya
welcome                to    digital    vidya

First one is the regular way with only one space between words, in the second case I have more than one space between words, in a third case I have some leading spaces along with a  couple of spaces between words and in the fourth case I have trailing spaces, you can see there are a couple of space after the last word.

Now, this could typically be the case if you get this data from a colleague or you get it from a text file or imported from a database.  So to clean this data and get rid of these extra spaces you can use the function trim.

Syntax: =TRIM(Text)

Trim function takes one  single argument which could either be the text which you type manually or it could be the cell reference, in this case, I will take the cell reference A1 and what this function does is it would  remove all the leading spaces and trailing spaces and extra spaces between words except one single space that is allowed.

So if I drag this down you would see that it has corrected all these texts. It has removed the extra space here between welcome into it has removed the leading spaces and trailing spaces.

2. Data Cleaning Techniques-Select and Treat All Blank Cells

If you just need to use the text you can convert it into values by using paste special I have student names here and their marks in three subjects. You can see that there are gaps in this dataset which could be because the student could not appear in the exam.

Now you may not want to leave this data set with blanks, you may want to type not appear in all these cells which are blank. So to do that you can either go and select each cell manually and type not appear. But if you have a  huge data set that because this could be very tiresome. So to do it at one go,

  • Select the entire data set,
  • Go to find and select and select this option Go to Special this opens the go-to special dialog box. You can also use the keyboard shortcut F5 and when you do this it opens the go-to dialog box here you have special button, click on it and it again opens it equal to special dialogue box

  • Click  blanks  and click okay, this would select all the blank cells in your data set at the same time

  • So now you have these cells in grey and the first cell is in white because this is the active cell so to type not appear in all these cells just start typing not appear and hit ctrl+enter and as soon as you hit ctrl+enter this gets entered in all the cells.

3. Data Cleaning Techniques-Convert Numbers Stored as Text into Numbers

Here I have this number  entered in  three different ways,


In the first case, it is a number as you can see it is aligned to the right of the cell numbers are always aligned to the right while text gets aligned to the left of a cell and in the other two cases, you can see  these are text format because these are  aligned to the left. now to convert all these three back into numbers.

The first one is already a number but to convert these two back into a number there are two ways to do it. The first one is I  would go to the formatting box and I  would type general and when I hit enter the second one gets converted back into a number because in this case it was merely in the text format but the  third case is a little more difficult  because it has been entered by using a  leading apostrophe and a lot of people  do this, a lot of people enter numbers  for starting with an apostrophe so that  it gets converted into a text and this  could create some problems.

A very foolproof method is type in any of the blank cells go to the cell and copy this now select these cells go to paste -> paste special and this opens the paste special dialog box. Here you have operation category within this select multiply and click okay so what this does is this multiplies this number with one and any number multiplied by one is unchanged but this also takes care of the apostrophe so now all these three numbers get converted back into a number format.

4. Data Cleaning Techniques-Remove Duplicates

Here I have a data set of students and  their marks in three subjects and there  are duplicates in this data so you can  see there is a duplicate for Bill and duplicate for Phil now if you want to  remove these duplicate values there are  two ways to do it first is using  conditional formatting,

  • So you can select the data set
  • Go to home -> conditional formatting
  • Highlight cell rules -> duplicate values and as soon as you select this it gives you the option to highlight duplicates and the formatting. I will keep the formatting as a red fill with dark red text and when I hit OK you can see that this has been highlighted and all those numbers and names that appear more than once it highlighted in red.

I can manually see that Phil repeats twice and Bill repeats twice so I can select this data and manually delete this.

The other way to remove duplicates & get cleaned data is by selecting the entire data set going to data and here I have the option remove duplicates I  click on this option and it opens the  remove duplicates dialog box here make  sure that if your data has headers  which in this case it has this option is  selected if this is not selected then  this is also counted as a part of your  data it should not be the case when you  have selected this option these names  are the names of the columns so I can  see that there is a student column math  column physics column in chemistry  column I can then select ok to remove  all those rows or all the data set which  is duplicate but in this case it would  not remove a number which repeats again  rather the entire row has to be an exact  duplicate so.

For example, Jack and these  three marks have to meet exactly the  numbers and name here Jack and these  three marks and if that is the case then  this row gets deleted similar is the  case with Jill and these numbers so now when I click OK it says one duplicate  values found and removed  unique  values remain the reason being that in  case of Jill you can see  that the marks do not match so this entire row is not an exact match and hence it remains but since in case of Bill it was an exact match then the  row was removed.

5. Data Cleaning Techniques-Highlight Errors

Here I have a dataset for five companies. I have their revenue number for three years and net income numbers for three years and using these numbers  I have calculated the net income margin which is net income by revenue.

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Now you can see that there are errors in data for Company X and Company Z, the reason being that there is no revenue number for these companies in and hence I get a division error because I  try to divide their net income by nothing. Now this is a small data set and  you can visually spot these errors but if you have a huge data set these  errors could be difficult to spot so to do that you can use two methods first is  using conditional formatting,

So select  this entire dataset go-to home -> conditional formatting and select new rule within new formatting rule dialog box select format only cells that contain and from this drop-down select errors when you select errors you would  get the option to format the cells which have error, in this case, let me select red and I click OK and as soon as I do  this all the cells that have errors in it get highlighted in red

We control Z  to go back the other way to do this would be to select those cells which  have errors and you can do this by using  the go-to special dialog box so to do  that press F5 this opens the go-to dialog box here you  have the special button, click on it,  this opens the go-to special dialog box.

Here select formulas and within formulas as soon as you selected all these four options get available, deselect the first three options and only keep the errors option selected and now click OK. When you do this all those cells which have error in it get selected now you can manually either delete all these cells or type something like not available and hit control enter so that it gets entered in all the cells which have error in.

6. Data Cleaning Techniques-Change Text to Lower/Upper/Proper Case

Here I have names written in different  ways you can see either it could be all caps, it could be all lowercase and in some cases, it’s a mix-and-match of uppercase lowercase so to make it all consistent you can use one of these three formulas,

LOWER() –  Converts all text into Lower Case.
ex. mary jane
UPPER() – Converts all text into Upper Case.
PROPER() – Converts all Text into Proper Case.
ex. Mary Jane

LOWER() formula takes one argument, it could be either the text that you type  in or you can use a cell reference in this case if I’ll use the cell reference A1 and when I hit ctrl enter this gives  me mary jane the name but all the  alphabets have been converted into  lowercase and when I drag this down this  is the case for all these names all  these names now look consistent in  lowercase you may want these all in the  uppercase so in that case you can use  the formula UPPER() and you can see this  these are all in uppercase now as I drag  this down the most used way is proper  case because it would keep the first  alphabet of your name as in capital and  the rest all would be in the lowercase  may show you I will select PROPER()  and I hit ctrl enter and you can see M of Mary and J of Jane is in caps  and rest all the alphabets are in the  lowercase and now I drag it down so  these are three formulas that can very  quickly make your text consistent this  could be the case when you are sharing a  worksheet or you get it from a text file  where a lot of people enter it in different ways these formulas can quickly make these consistent.

7. Data Cleaning Techniques-Spell Check

If you have huge data set and you want to only extract a part of it in the form of cleaned data while Microsoft PowerPoint and Microsoft Word have a feature where it would underline if there are any errors grammatical errors or spelling errors Microsoft Excel does not have that feature however you can still a run spellcheck and correct these errors.

So to do that select the data and press F7 and when you do that it runs the spellcheck for you and it is the same thing that you see in Microsoft Word or PowerPoint it will show you the text that it thinks is a spelling error and it will show you the suggestions as well so you can change these and once it is done it will show you that spellcheck is complete and you are good to go.

8. Data Cleaning Techniques-Delete all Formatting

If you have a worksheet where there is a lot of formatting and you need to clear  all the formatting you can quickly do that by,

  • Selecting the entire data
  • Go to Home –> Clear –> Clear Formats
  • You can also use clear all this would remove everything from your sheet including the content you can only clear the content would remain the formatting would remain intact you can clear the comments and the hyperlinks.

Data Cleansing Tools

Here are some interesting Data Cleansing tools relating to data cleaning techniques, analysis and modelling of data,

JASP – Open Source statistical software similar to SPSS with support of COS

Rattle – GUI for user-friendly machine learning with R

RapidMiner – Another point and click machine learning package

Orange – Open Source GUI for user-friendly machine learning with Python

Talend data preparation – Data cleaning, preparation tool with smarts

Trifacta Wranger – Data cleaning, preparation tool with the match by example feature

They are all open source or have free versions focusing on cleaning, analysing and modelling data.

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Data cleaning is an inherent part of the data science process to get cleaned data. In simple terms, you might divide data cleaning techniques down into four stages: collecting the data, cleaning the data, analyzing/modelling the data, and publishing the results to the relevant audience.

If you try to skip the data cleaning steps, you’ll often run into problems getting the raw data & not cleaned to work with traditional data cleansing tools for analysis in, say, R or Python. Thus, it becomes important to take into consideration, the data cleaning steps & data cleaning methods.

If you are looking forward to building a career in Data Science domain, enrol in our Data Science Using Python Course.

Image and concept credits

trumpexcel.com | P E X E L S

Aaron Tay from Blog – Musings about librarianship 

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