List has a date and amount, I need to create a cumulative amount by date

Question

I have a list which has a date and a amount, I need to create a list that has the cummulative total with the date.

I have the following result:

{{{2009, 8, 3}, 1829.}, {{2009, 8, 4}, 1113.}, {{2009, 8, 5}, 730.}, {{2009, 8, 6}, -243.}}

What I need:

 {{{2009, 8, 3}, 1829.}, {{2009, 8, 4}, 2942.}, {{2009, 8, 5}, 3672.}, {{2009, 8, 6}, 3429.}}

I have just spent over an hour trying to figure this out, any help is most appreciated.

Answer 1

list = {{{2009, 8, 3}, 1829.}, {{2009, 8, 4}, 1113.}, {{2009, 8, 5},730.}, {{2009, 8, 6}, -243.}}

Rest@FoldList[{#2[[1]], (#1 + #2)[[2]]} &, 0, list]

Or

Rest@FoldList[{#2[[1]], Last@Plus@## } &, 0, list]

Answer 2

Something like :

alist = {{{2009, 8, 3}, 1829.}, {{2009, 8, 4}, 1113.}, {{2009, 8, 5},730.}, {{2009, 8, 6}, -243.}};

Transpose[{alist[[All, 1]], Accumulate[alist[[All, 2]]]}]

Answer 3

Starting with:

list = {{{2009, 8, 3}, 1829.}, {{2009, 8, 4}, 1113.}, {{2009, 8, 5}, 730.}, {{2009, 8, 6}, -243.}};

I propose:

MapAt[Accumulate, list\[Transpose], 2]\[Transpose]

Which in the Notebook looks like:

Or with in-place modification:

list[[All, 2]] = Accumulate @ list[[All, 2]]; list