Add yAxisLabel prop to prepend text to horizontal labels.

App.js

@@ -117,6 +117,7 @@ export default class App extends React.Component {
                 data={data}
                 width={width}
                 height={height}
+                yAxisLabel={'$'}
                 chartConfig={chartConfig}
                 style={graphStyle}
                 onDataPointClick={({value, getColor}) =>
@@ -141,6 +142,7 @@ export default class App extends React.Component {
                 width={width}
                 height={height}
                 data={data}
+                yAxisLabel={'$'}
                 chartConfig={chartConfig}
                 style={graphStyle}
               />
@@ -160,6 +162,7 @@ export default class App extends React.Component {
                 data={data}
                 width={width}
                 height={height}
+                yAxisLabel={'$'}
                 chartConfig={chartConfig}
                 style={graphStyle}
               />

README.md

@@ -43,6 +43,7 @@ import {
     }}
     width={Dimensions.get('window').width} // from react-native
     height={220}
+    yAxisLabel={'$'}
     chartConfig={{
       backgroundColor: '#e26a00',
       backgroundGradientFrom: '#fb8c00',
@@ -120,6 +121,7 @@ const data = {
 | withShadow | boolean | Show shadow for line - default: True |
 | withInnerLines | boolean | Show inner dashed lines - default: True |
 | withOuterLines | boolean | Show outer dashed lines - default: True |
+| yAxisLabel | string | Prepend text to horizontal labels -- default: '' |
 | chartConfig | Object | Configuration object for the chart, see example config object above |
 |decorator | Function | This function takes a [whole bunch](https://github.com/indiespirit/react-native-chart-kit/blob/master/src/line-chart.js#L266) of stuff and can render extra elements, such as data point info or additional markup. |
 |onDataPointClick| Function| Callback that takes `{value, dataset, getColor}`|
@@ -184,6 +186,7 @@ const data = {
   data={data}
   width={screenWidth}
   height={220}
+  yAxisLabel={'$'}
   chartConfig={chartConfig}
 />
 ```
@@ -193,6 +196,7 @@ const data = {
 | data | Object | Data for the chart - see example above |
 | width | Number | Width of the chart, use 'Dimensions' library to get the width of your screen for responsive |
 | height | Number | Height of the chart |
+| yAxisLabel | string | Prepend text to horizontal labels -- default: '' |
 | chartConfig | Object | Configuration object for the chart, see example config in the beginning of this file |
 
 ## Pie chart

src/abstract-chart.js

@@ -47,8 +47,19 @@ class AbstractChart extends Component {
 
   renderHorizontalLabels = config => {
     const { count, data, height, paddingTop, paddingRight, yLabelsOffset = 12 } = config
-	var decimalPlaces = (this.props.chartConfig.decimalPlaces !== undefined) ? this.props.chartConfig.decimalPlaces : 2;
+    const decimalPlaces = this.props.chartConfig.decimalPlaces || 2;
+    const yAxisLabel = this.props.yAxisLabel || ''
+
     return [...new Array(count)].map((_, i) => {
+      let yLabel;
+
+      if(count === 1){ 
+        yLabel = `${yAxisLabel}${data[0].toFixed(decimalPlaces)}`
+      }else {
+       const label = (this.calcScaler(data) / (count - 1)) * i + Math.min(...data)
+       yLabel = `${yAxisLabel}${label.toFixed(decimalPlaces)}`
+      }
+
       return (
         <Text
           key={Math.random()}
@@ -57,7 +68,7 @@ class AbstractChart extends Component {
           y={(height * 3 / 4) - ((height - paddingTop) / count * i) + 12}
           fontSize={12}
           fill={this.props.chartConfig.color(0.5)}
-        >{count === 1 ? data[0].toFixed(decimalPlaces) : ((this.calcScaler(data) / (count - 1)) * i + Math.min(...data)).toFixed(decimalPlaces)}
+        >{yLabel}
         </Text>
       )
     })