Day 40, 2020-10-03Day 37&38&39, 2020-09-30 & 2020-10-01 & 2020-10-02Day 35 & Day 36, 2020-09-28 & 2020-09-29Day 34, 2020-09-27Day 33, 2020-09-26Day 32 (Task 10), 2020-09-25Day 31 (9-2-10), 2020-09-24Day Thirty (A puzzle to be solved), 2020-09-22Day Twenty Nine, 2020-09-22Day Twenty-Eight (Task 9-2-9), 2020-09-21Day Twenty-Seven, 2020-09-20Day Twenty Five, 2020-09-18Day Twenty Four, 2020-09-17Day Twenty Three (Task 9-2), 2020-09-16Day Twenty Two (Task 9-1 continued), 2020-09-15Day Twenty-One (Task 9-1 continued), 2020-09-14Day Twenty (Task 8 Continued + Task 9-1), 2020-09-13Day Nineteen (Task 8), Spet. 12, 2020Day Eighteen (Task 7-1-10, 11, Sept. 11, 2020Day Fourteen, Fifteen, Sixteen & Seventeen, Spet. 07 ~ 10, 2020Day Thirteen (Task 7-1), 2020-09-06Day Twelve, Sept. 5, 2020: ScalesDay Eleven, Sept.4th, 2020Day Ten (Task 6-6), Sept. 3rd, 2020Day Nine, 2020-09-02Day Eight, Spet. 1, 2020Day Six, 30 Aug 2020Day Five, 29 Aug 2020Day Four, 28 Aug 2020Day Three, 27 Aug 2020Day 1 & Day 2, 25 Aug. & 26 Aug., 2020, Basic Commands
Day Twenty Six, 2020-09-19
md`# Day Twenty Six, 2020-09-19`
md`
In Chapter 9, \`25_adding_values.html\`, assign a name of "previous_rects" to the rect generating codes before \`d3.select("p")\`. Then, modify the \`d3.select("p").on("click", function(){})\` this way, and explain what happens:
d3.select("p")
.on("click", function() {
var maxValue = 25;
var newNumber = Math.round(Math.random() * maxValue);
dataset.push(newNumber);
xScale.domain(d3.range(dataset.length))
yScale.domain([0, d3.max(dataset)]);
var bars = svg.selectAll("rect")
.data(dataset)
svg.selectAll("rect")
.data(dataset)
.enter()
.append("rect")
.attr("x", w / dataset.length)
.attr("y", function(d) {
return h - yScale(d);
})
.attr("width", xScale.bandwidth())
.attr("height", function(d) {
return yScale(d);
})
.attr("fill", "red")
.merge(previous_rects)
.transition()
.duration(500)
.attr("x", function(d, i){
return xScale(i);
})
.attr("y", function(d){
return h - yScale(d);
})
.attr("width", xScale.bandwidth())
.attr("height", function(d){
return yScale(d);
})
.style("fill", function(d){
return "rgb(0, 0, "+ Math.round(d * 10) +")"
});
});
Try to understand how the above codes worked.
`
md`
Modify the above codes this way, and explain what happens:
svg.selectAll("rect")
.data(dataset)
.enter()
.append("rect")
.attr("x", function(d, i){
return xScale(i);
})
.attr("y", function(d) {
return h - yScale(d);
})
.attr("width", xScale.bandwidth())
.attr("height", function(d) {
return yScale(d);
})
.attr("fill", "green")
.merge(previous_rects)
.transition()
.duration(500)
.attr("x", function(d, i){
return xScale(i);
})
.attr("y", function(d){
return h - yScale(d);
})
.attr("width", xScale.bandwidth())
.attr("height", function(d){
return yScale(d);
})
.style("fill", function(d){
return "rgb("+ Math.round(d * 10) +", "+ Math.round(d * 10) +", "+ Math.round(d * 10) +")"
});
`
md`
What I really don't get is why the newly generated bars sometimes are moving towards the left in comparison to previously generated bars? This literally drove me crazy!
I know that the \`.attr()\` right after \`.append("rect")\` are assigning attributions to the new generated bar (just one), rather than all the bars. And after \`.merge()\`, the \`attr()\` are assigning attributions to the bars in \`circles\` and the newly generated bar.
However, isn't the \`xScale(i)\` before \`.merge()\` equal to the \`xScale(i)\` after \`merge()\`? If yes, why are the positions of newly generated bars moving with the transition? If not, why aren't they equal??
`
md`
Go to [Day 27](https://observablehq.com/@hongtaoh/day-twenty-seven-2020-09-20).
`
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