Setting the file. One moment.
Subchapter 1.21
references/format-strings.mdMarkdown3 KBView on GitHub
Chart axis.format, labels.format, and DataTable column.format all accept d3-format (opens in a new tab) strings, plus a literal suffix extension.
Append non-format characters after a valid d3-format specifier. The engine tries d3-format first; if it fails, it splits off the trailing suffix and applies d3-format to the rest.
| Format | Input | Output | Use case |
|---|
".1f" | 12.5 | 12.5 | One decimal, no units |
".1f%" | 12.5 | 12.5% | Percentage (data already in %, not 0-1) |
".0f%" | 12 | 12% | Whole-number percentage |
"$,.0f" | 1234 | $1,234 | Currency with commas |
"$,.2f" | 3.75 | $3.75 | Currency with cents |
".1%" | 0.125 | 12.5% | d3 native percent (multiplies by 100) |
"~s" | 10000 | 10k | SI suffix (k, M, G) for large numbers |
"~s" | 1500000 | 1.5M | SI suffix, auto-scales |
"$~s" | 78000 | $78k | Currency with SI suffix. Caution: non-round thousands show decimals (60420 -> $60.42k). Round data values to clean thousands or use “$,.0f” for exact values |
",.0f" | 132979 | 132,979 | Comma-separated, no decimals |
When data is already in percentage form (e.g., 12.5 meaning 12.5%), use ".1f%" not ".1%". The d3 % type multiplies by 100, so 0.125 becomes 12.5% but 12.5 becomes 1,250.0%.
Format strings control what ticks look like. tickCount controls how many appear. Always pair them:
"axis": { "format": ".0f%", "tickCount": 5 }Without tickCount, many charts default to showing only the domain endpoints (e.g., 0% and 50%). This makes it nearly impossible for readers to identify specific data point values. Use 5-6 ticks as a default for most charts. The engine treats tickCount as a suggestion and picks clean round values nearby.
Use labels.prefix to prepend a literal string before each formatted label value. Applied after d3-format, so it won’t interfere with format parsing. Works on bar, column, and dot charts.
"labels": { "format": ",.0f", "prefix": "$" }This produces labels like $1,234. For cases where d3-format already handles the prefix (like "$,.0f"), you don’t need labels.prefix.
When the format string already includes units (%, $, k), drop the units from axis.title. Write "Chronic absence rate" with format: ".0f%", not "Chronic absence rate (%)". The ticks themselves show 10%, 20%, 30%, which makes (%) in the title redundant.