For loop working but errors when I convert to reduce function with JavaScript
This is working:
const messagesOrganised = {};
for (const msg of messagesGroupedByName) {
if (!messagesOrganised[msg.groupBy]) {
messagesOrganised[msg.groupBy] = [msg];
} else {
messagesOrganised[msg.groupBy].push(msg);
}
}
But when I try and convert it to using the reduce function I get an error:
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
}, {});
TypeError: Cannot read property 'Name' of undefined
javascript functional-programming
edited Nov 13 '18 at 6:42
Ouroborus
6,2871533
asked Nov 13 '18 at 6:07
Evans
4,22541157276
add a comment |
This is working:
const messagesOrganised = {};
for (const msg of messagesGroupedByName) {
if (!messagesOrganised[msg.groupBy]) {
messagesOrganised[msg.groupBy] = [msg];
} else {
messagesOrganised[msg.groupBy].push(msg);
}
}
But when I try and convert it to using the reduce function I get an error:
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
}, {});
TypeError: Cannot read property 'Name' of undefined
javascript functional-programming
edited Nov 13 '18 at 6:42
Ouroborus
6,2871533
asked Nov 13 '18 at 6:07
Evans
4,22541157276
1
You need to returnaccSo it’s available on the next iteration.
– Mark Meyer
Nov 13 '18 at 6:16
Well, just don't usereduce? There's no advantage to it here.
– Bergi
Nov 13 '18 at 9:08
@Bergi, don't use it, because I don't understand it - maybe ok when you hitting deadline with a project, but definitely not very good approach here ;)
– Fabio
Nov 13 '18 at 10:31
add a comment |
This is working:
const messagesOrganised = {};
for (const msg of messagesGroupedByName) {
if (!messagesOrganised[msg.groupBy]) {
messagesOrganised[msg.groupBy] = [msg];
} else {
messagesOrganised[msg.groupBy].push(msg);
}
}
But when I try and convert it to using the reduce function I get an error:
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
}, {});
TypeError: Cannot read property 'Name' of undefined
javascript functional-programming
edited Nov 13 '18 at 6:42
Ouroborus
6,2871533
asked Nov 13 '18 at 6:07
Evans
4,22541157276
This is working:
const messagesOrganised = {};
for (const msg of messagesGroupedByName) {
if (!messagesOrganised[msg.groupBy]) {
messagesOrganised[msg.groupBy] = [msg];
} else {
messagesOrganised[msg.groupBy].push(msg);
}
}
But when I try and convert it to using the reduce function I get an error:
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
}, {});
TypeError: Cannot read property 'Name' of undefined
javascript functional-programming
javascript functional-programming
edited Nov 13 '18 at 6:42
Ouroborus
6,2871533
asked Nov 13 '18 at 6:07
Evans
4,22541157276
edited Nov 13 '18 at 6:42
Ouroborus
6,2871533
asked Nov 13 '18 at 6:07
Evans
4,22541157276
edited Nov 13 '18 at 6:42
Ouroborus
6,2871533
edited Nov 13 '18 at 6:42
Ouroborus
6,2871533
edited Nov 13 '18 at 6:42
Ouroborus
6,2871533
6,2871533
asked Nov 13 '18 at 6:07
Evans
4,22541157276
asked Nov 13 '18 at 6:07
Evans
4,22541157276
asked Nov 13 '18 at 6:07
Evans
4,22541157276
4,22541157276
1
You need to returnaccSo it’s available on the next iteration.
– Mark Meyer
Nov 13 '18 at 6:16
Well, just don't usereduce? There's no advantage to it here.
– Bergi
Nov 13 '18 at 9:08
@Bergi, don't use it, because I don't understand it - maybe ok when you hitting deadline with a project, but definitely not very good approach here ;)
– Fabio
Nov 13 '18 at 10:31
add a comment |
1
You need to returnaccSo it’s available on the next iteration.
– Mark Meyer
Nov 13 '18 at 6:16
Well, just don't usereduce? There's no advantage to it here.
– Bergi
Nov 13 '18 at 9:08
@Bergi, don't use it, because I don't understand it - maybe ok when you hitting deadline with a project, but definitely not very good approach here ;)
– Fabio
Nov 13 '18 at 10:31
1
1
You need to return
acc So it’s available on the next iteration.– Mark Meyer
Nov 13 '18 at 6:16
You need to return
acc So it’s available on the next iteration.– Mark Meyer
Nov 13 '18 at 6:16
Well, just don't use
reduce? There's no advantage to it here.– Bergi
Nov 13 '18 at 9:08
Well, just don't use
reduce? There's no advantage to it here.– Bergi
Nov 13 '18 at 9:08
@Bergi, don't use it, because I don't understand it - maybe ok when you hitting deadline with a project, but definitely not very good approach here ;)
– Fabio
Nov 13 '18 at 10:31
@Bergi, don't use it, because I don't understand it - maybe ok when you hitting deadline with a project, but definitely not very good approach here ;)
– Fabio
Nov 13 '18 at 10:31
add a comment |
2 Answers
2
active
oldest
votes
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
return acc; // return the working object
}, {});
reduce doesn't track your working object automatically. You need to return something in each iteration of reduce, usually your working object. That something will get passed to the next iteration.
answered Nov 13 '18 at 6:46
Ouroborus
6,2871533
1
The concept of a "working object" that gets mutated does totally contradict the idea behindreducethough :-P
– Bergi
Nov 13 '18 at 9:09
add a comment |
Please refer to how
Array.reduce()works:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce#How_reduce()_works
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
return acc; // <<<< You need to return accumulated value from callback
});
Let me know if this helps.
answered Nov 13 '18 at 6:45
AkshayM
675314
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
return acc; // return the working object
}, {});
reduce doesn't track your working object automatically. You need to return something in each iteration of reduce, usually your working object. That something will get passed to the next iteration.
answered Nov 13 '18 at 6:46
Ouroborus
6,2871533
1
The concept of a "working object" that gets mutated does totally contradict the idea behindreducethough :-P
– Bergi
Nov 13 '18 at 9:09
add a comment |
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
return acc; // return the working object
}, {});
reduce doesn't track your working object automatically. You need to return something in each iteration of reduce, usually your working object. That something will get passed to the next iteration.
answered Nov 13 '18 at 6:46
Ouroborus
6,2871533
1
The concept of a "working object" that gets mutated does totally contradict the idea behindreducethough :-P
– Bergi
Nov 13 '18 at 9:09
add a comment |
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
return acc; // return the working object
}, {});
reduce doesn't track your working object automatically. You need to return something in each iteration of reduce, usually your working object. That something will get passed to the next iteration.
answered Nov 13 '18 at 6:46
Ouroborus
6,2871533
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
return acc; // return the working object
}, {});
reduce doesn't track your working object automatically. You need to return something in each iteration of reduce, usually your working object. That something will get passed to the next iteration.
answered Nov 13 '18 at 6:46
Ouroborus
6,2871533
answered Nov 13 '18 at 6:46
Ouroborus
6,2871533
answered Nov 13 '18 at 6:46
Ouroborus
6,2871533
answered Nov 13 '18 at 6:46
Ouroborus
6,2871533
6,2871533
1
The concept of a "working object" that gets mutated does totally contradict the idea behindreducethough :-P
– Bergi
Nov 13 '18 at 9:09
add a comment |
1
The concept of a "working object" that gets mutated does totally contradict the idea behindreducethough :-P
– Bergi
Nov 13 '18 at 9:09
1
1
The concept of a "working object" that gets mutated does totally contradict the idea behind
reduce though :-P– Bergi
Nov 13 '18 at 9:09
The concept of a "working object" that gets mutated does totally contradict the idea behind
reduce though :-P– Bergi
Nov 13 '18 at 9:09
add a comment |
Please refer to how
Array.reduce()works:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce#How_reduce()_works
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
return acc; // <<<< You need to return accumulated value from callback
});
Let me know if this helps.
answered Nov 13 '18 at 6:45
AkshayM
675314
add a comment |
Please refer to how
Array.reduce()works:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce#How_reduce()_works
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
return acc; // <<<< You need to return accumulated value from callback
});
Let me know if this helps.
answered Nov 13 '18 at 6:45
AkshayM
675314
add a comment |
Please refer to how
Array.reduce()works:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce#How_reduce()_works
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
return acc; // <<<< You need to return accumulated value from callback
});
Let me know if this helps.
answered Nov 13 '18 at 6:45
AkshayM
675314
Please refer to how
Array.reduce()works:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce#How_reduce()_works
const messagesOrganised = messagesGroupedByName.reduce((acc, msg) => {
if (!acc[msg.groupBy]) {
acc[msg.groupBy] = [msg];
} else {
acc[msg.groupBy].push(msg);
}
return acc; // <<<< You need to return accumulated value from callback
});
Let me know if this helps.
answered Nov 13 '18 at 6:45
AkshayM
675314
answered Nov 13 '18 at 6:45
AkshayM
675314
answered Nov 13 '18 at 6:45
AkshayM
675314
answered Nov 13 '18 at 6:45
AkshayM
675314
675314
add a comment |
add a comment |
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1
You need to return
accSo it’s available on the next iteration.– Mark Meyer
Nov 13 '18 at 6:16
Well, just don't use
reduce? There's no advantage to it here.– Bergi
Nov 13 '18 at 9:08
@Bergi, don't use it, because I don't understand it - maybe ok when you hitting deadline with a project, but definitely not very good approach here ;)
– Fabio
Nov 13 '18 at 10:31