Explanation of “usecols do not match columns, columns expected but not found” with examples:
The error message “usecols do not match columns, columns expected but not found” typically occurs when you are trying to read data from a file using a specific set of column names or indices, but the file does not contain all of the expected columns or the columns are not in the correct order.
This error commonly occurs when reading data from a CSV file using a library or function like pandas’ read_csv(). The usecols parameter is used to specify which columns from the file you want to read. However, if the specified columns are not found in the file, you will encounter this error.
Example 1:
Let’s consider a CSV file named data.csv with the following contents:
Name,Age,City
John,25,New York
Alice,30,San Francisco
Bob,35,Los Angeles
If you try to read this file and specify the usecols=['Name', 'Age', 'Salary'] parameter, you will encounter the “usecols do not match columns, columns expected but not found” error. This is because the column “Salary” does not exist in the file. To fix this error, you should either remove the “Salary” column from the usecols parameter or add the “Salary” column to the file.
Example 2:
Let’s consider another case where the columns exist in the file but are not in the correct order. Assuming the same data.csv file as before, if you try to read the file with the usecols=['Age', 'Name', 'City'] parameter, you will encounter the same error message. This is because the columns in the file are in the order “Name, Age, City”, but you specified the order as “Age, Name, City”. To fix this error, make sure the column order in the usecols parameter matches the order of the columns in the file.
Conclusion:
The “usecols do not match columns, columns expected but not found” error occurs when the specified columns in a file do not match the actual columns present in the file. Make sure to check the column names, order, and existence to resolve this error.