Home > Articles

  • Print
  • + Share This
This chapter is from the book

6.2 Columns Contain Values, Not Variables

Data can have columns that contain values instead of variables. This is usually a convenient format for data collection and presentation.

6.2.1 Keep One Column Fixed

We’ll use data on income and religion in the United States from the Pew Research Center to illustrate how to work with columns that contain values, rather than variables.

import pandas as pd
pew = pd.read_csv('../data/pew.csv')

When we look at this data set, we can see that not every column is a variable. The values that relate to income are spread across multiple columns. The format shown is a great choice when presenting data in a table, but for data analytics, the table needs to be reshaped so that we have religion, income, and count variables.

# show only the first few columns
print(pew.iloc[:, 0:6])
                   religion  <$10k  $10-20k  $20-30k  $30-40k  0                  Agnostic     27       34       60       81
1                   Atheist     12       27       37       52
2                  Buddhist     27       21       30       34
3                  Catholic    418      617      732      670
4        Don't know/refused     15       14       15       11
5          Evangelical Prot    575      869     1064      982
6                     Hindu      1        9        7        9
7   Historically Black Prot    228      244      236      238
8         Jehovah's Witness     20       27       24       24
9                    Jewish     19       19       25       25
10            Mainline Prot    289      495      619      655
11                   Mormon     29       40       48       51
12                   Muslim      6        7        9       10
13                 Orthodox     13       17       23       32
14          Other Christian      9        7       11       13
15             Other Faiths     20       33       40       46
16    Other World Religions      5        2        3        4
17             Unaffiliated    217      299      374      365

0        76
1        35
2        33
3       638
4        10
5       881
6        11
7       197
8        21
9        30
10      651
11       56
12        9
13       32
14       13
15       49
16        2
17      341

This view of the data is also known as “wide” data. To turn it into the “long” tidy data format, we will have to unpivot/melt/gather (depending on which statistical programming language we use) our dataframe. Pandas has a function called melt that will reshape the dataframe into a tidy format. melt takes a few parameters:

  • id_vars is a container (list, tuple, ndarray) that represents the variables that will remain as is.

  • value_vars identifies the columns you want to melt down (or unpivot). By default, it will melt all the columns not specified in the id_vars parameter.

  • var_name is a string for the new column name when the value_vars is melted down. By default, it will be called variable.

  • value_name is a string for the new column name that represents the values for the var_name. By default, it will be called value.

# we do not need to specify a value_vars since we want to pivot
# all the columns except for the 'religion' column
pew_long = pd.melt(pew, id_vars='religion')

             religion variable  value
0            Agnostic    <$10k     27
1             Atheist    <$10k     12
2            Buddhist    <$10k     27
3            Catholic    <$10k    418
4  Don't know/refused    <$10k     15
                  religion            variable  value
175               Orthodox  Don't know/refused     73
176        Other Christian  Don't know/refused     18
177           Other Faiths  Don't know/refused     71
178  Other World Religions  Don't know/refused      8
179           Unaffiliated  Don't know/refused    597

We can change the defaults so that the melted/unpivoted columns are named.

pew_long = pd.melt(pew,
             religion income  count
0            Agnostic  <$10k     27
1             Atheist  <$10k     12
2            Buddhist  <$10k     27
3            Catholic  <$10k    418
4  Don't know/refused  <$10k     15
                  religion              income  count
175               Orthodox  Don't know/refused     73
176        Other Christian  Don't know/refused     18
177           Other Faiths  Don't know/refused     71
178  Other World Religions  Don't know/refused      8
179           Unaffiliated  Don't know/refused    597

6.2.2 Keep Multiple Columns Fixed

Not every data set will have one column to hold still while you unpivot the rest of the columns. As an example, consider the Billboard data set.

billboard = pd.read_csv('../data/billboard.csv')

# look at the first few rows and columns
print(billboard.iloc[0:5, 0:16])
   year        artist                    track  time date.entered  0  2000         2 Pac  Baby Don't Cry (Keep...  4:22   2000-02-26
1  2000       2Ge+her  The Hardest Part Of ...  3:15   2000-09-02
2  2000  3 Doors Down               Kryptonite  3:53   2000-04-08
3  2000  3 Doors Down                    Loser  4:24   2000-10-21
4  2000      504 Boyz            Wobble Wobble  3:35   2000-04-15
   wk1   wk2   wk3   wk4   wk5   wk6   wk7   wk8   wk9  wk10  wk11
0   87  82.0  72.0  77.0  87.0  94.0  99.0   NaN   NaN   NaN   NaN
1   91  87.0  92.0   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN
2   81  70.0  68.0  67.0  66.0  57.0  54.0  53.0  51.0  51.0  51.0
3   76  76.0  72.0  69.0  67.0  65.0  55.0  59.0  62.0  61.0  61.0
4   57  34.0  25.0  17.0  17.0  31.0  36.0  49.0  53.0  57.0  64.0

You can see here that each week has its own column. Again, there is nothing wrong with this form of data. It may be easy to enter the data in this form, and it is much quicker to understand what it means when the data is presented in a table. However, there may be a time when you will need to melt the data. For example, if you wanted to create a faceted plot of the weekly ratings, the facet variable would need to be a column in the dataframe.

billboard_long = pd.melt(
    id_vars=['year', 'artist', 'track', 'time', 'date.entered'],
   year        artist                    track  time date.entered  0  2000         2 Pac  Baby Don't Cry (Keep...  4:22   2000-02-26
1  2000       2Ge+her  The Hardest Part Of ...  3:15   2000-09-02
2  2000  3 Doors Down               Kryptonite  3:53   2000-04-08
3  2000  3 Doors Down                    Loser  4:24   2000-10-21
4  2000      504 Boyz            Wobble Wobble  3:35   2000-04-15

  week  rating
0  wk1    87.0
1  wk1    91.0
2  wk1    81.0
3  wk1    76.0
4  wk1    57.0
       year            artist                    track  time  24087  2000       Yankee Grey     Another Nine Minutes  3:10
24088  2000  Yearwood, Trisha          Real Live Woman  3:55
24089  2000   Ying Yang Twins  Whistle While You Tw...  4:19
24090  2000     Zombie Nation            Kernkraft 400  3:30
24091  2000   matchbox twenty                     Bent  4:12

      date.entered  week rating
24087   2000-04-29  wk76    NaN
24088   2000-04-01  wk76    NaN
24089   2000-03-18  wk76    NaN
24090   2000-09-02  wk76    NaN
24091   2000-04-29  wk76    NaN
  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020