GPandas
DataFrame Basics

DataFrame Operations

Select columns, rename, display, and export DataFrames

Learn the essential DataFrame operations for manipulating and transforming your data in GPandas.

Overview

GPandas DataFrames support several core operations:

OperationMethod(s)Description
Column SelectionSelect(), SelectCol()Extract specific columns
RenamingRename()Change column names
DisplayString()Pretty-print as table
ExportToCSV()Save to CSV format

Column Selection

GPandas provides two methods for selecting columns from a DataFrame.

Select() - Multiple Columns

Returns a new DataFrame containing only the specified columns.

func (df *DataFrame) Select(columns ...string) (*DataFrame, error)

Parameters

ParameterTypeDescription
columns...stringOne or more column names to select

Example

package main

import (
    "fmt"
    "log"

    "github.com/apoplexi24/gpandas"
)

func main() {
    gp := gpandas.GoPandas{}
    
    // Load sample data
    df, _ := gp.Read_csv("employees.csv")
    
    fmt.Println("Original DataFrame:")
    fmt.Println(df.String())
    
    // Select specific columns
    subset, err := df.Select("name", "department", "salary")
    if err != nil {
        log.Fatalf("Selection failed: %v", err)
    }
    
    fmt.Println("\nSelected Columns:")
    fmt.Println(subset.String())
}

Output

Original DataFrame:
+------+-------------+--------+-------+
| name | department  | salary | years |
+------+-------------+--------+-------+
| Alice| Engineering | 85000  | 5     |
| Bob  | Marketing   | 72000  | 3     |
+------+-------------+--------+-------+
[2 rows x 4 columns]

Selected Columns:
+------+-------------+--------+
| name | department  | salary |
+------+-------------+--------+
| Alice| Engineering | 85000  |
| Bob  | Marketing   | 72000  |
+------+-------------+--------+
[2 rows x 3 columns]

SelectCol() - Single Column as Series

Returns a single column as a Series reference (not a DataFrame).

func (df *DataFrame) SelectCol(column string) (*collection.Series, error)

Example

// Get a single column as Series
salarySeries, err := df.SelectCol("salary")
if err != nil {
    log.Fatalf("Column not found: %v", err)
}

// Access individual values
firstSalary, _ := salarySeries.At(0)
fmt.Printf("First salary: %v\n", firstSalary)

// Get series length
fmt.Printf("Total entries: %d\n", salarySeries.Len())

Selection Data Flow

Renaming Columns

The Rename() method changes column names while preserving column order and data.

Function Signature

func (df *DataFrame) Rename(columns map[string]string) error

Parameters

ParameterTypeDescription
columnsmap[string]stringMap of old names to new names

Example

package main

import (
    "fmt"
    "log"

    "github.com/apoplexi24/gpandas"
)

func main() {
    gp := gpandas.GoPandas{}
    df, _ := gp.Read_csv("data.csv")
    
    fmt.Println("Before renaming:")
    fmt.Println(df.String())
    
    // Rename columns
    err := df.Rename(map[string]string{
        "emp_name":   "employee_name",
        "dept":       "department",
        "sal":        "salary",
    })
    if err != nil {
        log.Fatalf("Rename failed: %v", err)
    }
    
    fmt.Println("\nAfter renaming:")
    fmt.Println(df.String())
}

Rename Behavior

ScenarioBehavior
Valid columnRenamed successfully
Non-existent columnError returned
Empty mapError returned
Partial renameOnly specified columns renamed

Error Handling

err := df.Rename(map[string]string{
    "nonexistent_column": "new_name",
})
if err != nil {
    // Error: "the column 'nonexistent_column' is not present in DataFrame"
    log.Printf("Rename error: %v", err)
}

Display with String()

The String() method returns a formatted table representation of the DataFrame.

Function Signature

func (df *DataFrame) String() string

Features

FeatureDescription
ASCII table formatUses +, -, `
Auto-column sizingColumns adjust to content width
Row limitingShows first 10 rows for large DataFrames
Dimension infoDisplays [rows x columns] summary

Example Output

+---------+-------------+--------+
| name    | department  | salary |
+---------+-------------+--------+
| Alice   | Engineering | 85000  |
| Bob     | Marketing   | 72000  |
| Charlie | Engineering | 92000  |
+---------+-------------+--------+
[3 rows x 3 columns]

Large DataFrame Display

For DataFrames with more than 10 rows:

+---------+-------------+--------+
| name    | department  | salary |
+---------+-------------+--------+
| Row 1   | ...         | ...    |
| Row 2   | ...         | ...    |
| ...     | ...         | ...    |
| Row 10  | ...         | ...    |
+---------+-------------+--------+
Showing first 10 rows of 1000 rows x 3 columns

Export with ToCSV()

The ToCSV() method exports DataFrame contents to CSV format.

Function Signature

func (df *DataFrame) ToCSV(filepath string, separator ...string) (string, error)

Parameters

ParameterTypeDescriptionDefault
filepathstringOutput file path (empty for string output)-
separatorstringColumn separator,

Returns

ReturnWhen
(string, nil)filepath is empty - returns CSV as string
("", nil)filepath is provided - writes to file
("", error)Operation failed

Export to File

// Export with default comma separator
_, err := df.ToCSV("output/data.csv")
if err != nil {
    log.Fatalf("Export failed: %v", err)
}

// Export with custom separator (tab-separated)
_, err = df.ToCSV("output/data.tsv", "\t")
if err != nil {
    log.Fatalf("Export failed: %v", err)
}

// Export with semicolon (European format)
_, err = df.ToCSV("output/data_eu.csv", ";")
if err != nil {
    log.Fatalf("Export failed: %v", err)
}

Export to String

// Get CSV as string (pass empty filepath)
csvString, err := df.ToCSV("", ",")
if err != nil {
    log.Fatalf("Export failed: %v", err)
}

fmt.Println("CSV Content:")
fmt.Println(csvString)

// Use the string for other purposes
// e.g., send via API, write to custom location, etc.

CSV Output Format

name,department,salary,years
Alice,Engineering,85000,5
Bob,Marketing,72000,3
Charlie,Engineering,92000,7

Operations Pipeline

Combine operations for complex transformations:

Complete Pipeline Example

package main

import (
    "fmt"
    "log"

    "github.com/apoplexi24/gpandas"
)

func main() {
    gp := gpandas.GoPandas{}
    
    // Step 1: Load data
    df, err := gp.Read_csv("raw_data.csv")
    if err != nil {
        log.Fatalf("Load failed: %v", err)
    }
    fmt.Println("Step 1 - Loaded:")
    fmt.Println(df.String())
    
    // Step 2: Select relevant columns
    df, err = df.Select("emp_id", "emp_name", "dept", "sal")
    if err != nil {
        log.Fatalf("Select failed: %v", err)
    }
    fmt.Println("\nStep 2 - Selected:")
    fmt.Println(df.String())
    
    // Step 3: Rename for clarity
    err = df.Rename(map[string]string{
        "emp_id":   "employee_id",
        "emp_name": "name",
        "dept":     "department",
        "sal":      "salary",
    })
    if err != nil {
        log.Fatalf("Rename failed: %v", err)
    }
    fmt.Println("\nStep 3 - Renamed:")
    fmt.Println(df.String())
    
    // Step 4: Export cleaned data
    _, err = df.ToCSV("cleaned_data.csv", ",")
    if err != nil {
        log.Fatalf("Export failed: %v", err)
    }
    fmt.Println("\nStep 4 - Exported to cleaned_data.csv")
}

Thread Safety

All DataFrame operations are thread-safe:

MethodLock TypeDescription
Select()RLockRead lock for concurrent reads
SelectCol()RLockRead lock for concurrent reads
Rename()LockWrite lock for exclusive access
String()NoneUses column data directly
ToCSV()NoneUses column data directly

Concurrent Access Example

package main

import (
    "fmt"
    "sync"

    "github.com/apoplexi24/gpandas"
)

func main() {
    gp := gpandas.GoPandas{}
    df, _ := gp.Read_csv("data.csv")
    
    var wg sync.WaitGroup
    
    // Multiple goroutines can read simultaneously
    for i := 0; i < 5; i++ {
        wg.Add(1)
        go func(id int) {
            defer wg.Done()
            
            // Safe concurrent read
            subset, _ := df.Select("name", "salary")
            fmt.Printf("Goroutine %d: %d rows\n", id, len(subset.Index))
        }(i)
    }
    
    wg.Wait()
}

Error Reference

ErrorCauseSolution
"DataFrame is nil"Operating on nil DataFrameCheck DataFrame initialization
"column 'X' not found"Invalid column nameVerify column exists
"columns slice is empty"Empty map to RenameProvide at least one column
"failed to write CSV"File system errorCheck permissions and path

See Also

Creating DataFrames

Build DataFrames from in-memory data using the DataFrame constructor

Adding Columns

Add, replace, compute, and insert DataFrame columns in place with Assign, AssignFunc, and Insert

On this page

OverviewColumn SelectionSelect() - Multiple ColumnsParametersExampleOutputSelectCol() - Single Column as SeriesExampleSelection Data FlowRenaming ColumnsFunction SignatureParametersExampleRename BehaviorError HandlingDisplay with String()Function SignatureFeaturesExample OutputLarge DataFrame DisplayExport with ToCSV()Function SignatureParametersReturnsExport to FileExport to StringCSV Output FormatOperations PipelineComplete Pipeline ExampleThread SafetyConcurrent Access ExampleError ReferenceSee Also