re-usable component to show quantity with significant decimal digits

* used in line analysis table
* can pass the maximum number of decimal digits (which becomes the default if no uncertainty is passed)
* if uncertainty is passed, both the value and uncertainty are rounded to the second significant digit in the uncertainties
* might not be entirely perfect - javascript treatment of numbers can be a bit funny... but the full underlying floats are untouched via the API

CHANGES.rst

@@ -56,6 +56,8 @@ Other Changes and Additions
 
 - Data dropdowns in plugins are now filtered to only applicable entries. [#1221]
 
+- Reported quantities are rounded/truncated to avoid showing unnecessary precision. [#1244]
+
 2.4 (2022-03-29)
 ================
 

jdaviz/app.py

@@ -73,6 +73,10 @@
                                     os.path.join(os.path.dirname(__file__),
                                                  'components/plugin_section_header.vue'))
 
+ipyvue.register_component_from_file(None, 'j-number-uncertainty',
+                                    os.path.join(os.path.dirname(__file__),
+                                                 'components/number_uncertainty.vue'))
+
 ipyvue.register_component_from_file(None, 'plugin-dataset-select',
                                     os.path.join(os.path.dirname(__file__),
                                                  'components/plugin_dataset_select.vue'))

jdaviz/components/number_uncertainty.vue

@@ -0,0 +1,42 @@
+<template>
+  <span>
+    {{ valueTrunc }} {{ uncertainty ? "&#177; " + uncertTrunc : null}} {{ unit }}
+  </span>
+</template>
+
+<script>
+
+module.exports = {
+  data: function () {
+    const maxDecs = this.maxDecs || 5;
+    var nDecs = maxDecs;
+    var uncertTrunc = null;
+
+    if (this.uncertainty !== '') {
+      // then uncertainty was provided, so let's round both the uncertainty and value
+      // to show up to the second significant digit in the uncertainty.
+      nDecs = 2 - Math.log10(parseFloat(this.uncertainty));
+      if (nDecs > maxDecs) {
+        nDecs = maxDecs
+      } else if (nDecs < 0) {
+        // NOTE: could support rounding of integers to less significant digits, but for now
+        // we'll at least show all digits before the decimal.
+        nDecs = 0
+      }
+
+      uncertTrunc = +parseFloat(this.uncertainty).toFixed(nDecs)
+    }
+
+    const valueTrunc = +parseFloat(this.value).toFixed(nDecs);
+
+    return {
+      nDecs: nDecs,
+      valueTrunc: valueTrunc,
+      uncertTrunc: uncertTrunc
+    }
+  },
+  props: ['value', 'uncertainty', 'unit', 'maxDecs'],
+  methods: {
+  }
+};
+</script>

jdaviz/configs/specviz/plugins/line_analysis/line_analysis.vue

@@ -84,7 +84,14 @@
               </a> 
             </j-tooltip>
           </v-col>
-          <v-col cols=6>{{ item.result }} {{ item.uncertainty ? "&#177; " + item.uncertainty : null}} {{ item.unit }}</v-col>
+          <v-col cols=6>
+            <j-number-uncertainty
+              :value="item.result"
+              :uncertainty="item.uncertainty"
+              :unit="item.unit"
+              :maxDecs="5"
+            ></j-number-uncertainty>
+          </v-col>
         </v-row>
       </div>
       <div v-if="results_computing"