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spreadsheets.md

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+# Spreadsheets Deep Dive
+
+## Formula Patterns
+
+### Lookup Values
+```
+=VLOOKUP(lookup_value, table_range, column_index, FALSE)
+=XLOOKUP(lookup_value, lookup_array, return_array)  [Excel 365+]
+=INDEX(return_range, MATCH(lookup_value, lookup_range, 0))
+```
+
+### Conditional Calculations
+```
+=SUMIF(range, criteria, sum_range)
+=SUMIFS(sum_range, criteria_range1, criteria1, criteria_range2, criteria2)
+=COUNTIF(range, criteria)
+=AVERAGEIF(range, criteria, average_range)
+```
+
+### Text Manipulation
+```
+=CONCATENATE(A1, " ", B1)  or  =A1 & " " & B1
+=LEFT(text, num_chars)
+=RIGHT(text, num_chars)
+=TRIM(text)  -- removes extra spaces
+=PROPER(text)  -- Title Case
+```
+
+### Date Functions
+```
+=TODAY()
+=YEAR(date) / MONTH(date) / DAY(date)
+=DATEDIF(start_date, end_date, "Y")  -- years between dates
+=WORKDAY(start_date, num_days)  -- excludes weekends
+```
+
+---
+
+## Pivot Tables
+
+**When to use:** Summarizing large datasets by categories.
+
+**Setup:**
+1. Select data (including headers)
+2. Insert → Pivot Table
+3. Drag fields:
+   - Rows = categories to group by
+   - Columns = secondary grouping
+   - Values = what to calculate (Sum, Count, Average)
+
+**Refresh:** Right-click pivot → Refresh (data source changed)
+
+**Calculated fields:** Add custom calculations within pivot.
+
+---
+
+## Common Errors & Fixes
+
+| Error | Cause | Fix |
+|-------|-------|-----|
+| #N/A | VLOOKUP can't find value | Check spelling, spaces, data type |
+| #REF! | Referenced cell deleted | Update formula references |
+| #VALUE! | Wrong data type | Check if text vs number |
+| #DIV/0! | Dividing by zero | Add IF to check denominator |
+| ##### | Column too narrow | Widen column |
+
+---
+
+## Data Cleaning
+
+**Remove duplicates:** Data → Remove Duplicates
+**Text to columns:** Data → Text to Columns (split by delimiter)
+**Find & Replace:** Ctrl+H, use wildcards (* for any characters)
+**Trim spaces:** `=TRIM(A1)` then paste values
+
+---
+
+## Keyboard Shortcuts (Excel)
+
+| Action | Windows | Mac |
+|--------|---------|-----|
+| New row/column | Ctrl++ | Cmd++ |
+| Delete row/column | Ctrl+- | Cmd+- |
+| Fill down | Ctrl+D | Cmd+D |
+| Absolute reference | F4 | Cmd+T |
+| Go to formula cell | Ctrl+[ | Cmd+[ |
+| Select to end | Ctrl+Shift+End | Cmd+Shift+End |