pack well it’s Monday again for you guys
or me it’s Saturday evening and there is
a lot of hiking here behind me this
episode will be released automatically
to you guys on Monday while I am in a
canoe traversing the Swedish wilderness
last time I showed you a basic example
of reduce where we used it to summarize
the property of any series of objects
however reduce is not limited to
reducing a list to a number it can
reduce it to anything such as another
array or an object and that is what
we’re gonna do today I’m also gonna
throw a couple of other higher-order
functions into the mix up top previously
about how higher-order functions can
post very well together and I’m gonna
give you some more examples of this day
we’re gonna jump right into it on the
left side of the screen we see data dot
txt this is a tab separated file so
there is ABS here it’s ABS OH
steps
here and here and this is just some file
that we got out of some old system we
having assigned a task we are going to
turn it into something that looks a
little bit like this so we’re going to
turn it into a object literal and every
key and that object is going to be named
so Mark Johnson Mark Johnson here that’s
the same guy and his words or or order
items or whatever those are goes in an
array
so these orders going to be turned into
these so the first first the string have
a pretty string after the the item name
is the price of the item and the second
integer after the name of the item it’s
going to be the quantity of that this is
our mission
because we’re dealing with a file here
we need to import the FS namespace from
no I’m going to use a new require syntax
normally you would do something like
this but we are going to use modern
JavaScript which means that
yes so these are the same thing but
we’re gonna use this one now to read
from the file we just go FS not weed
file sir
beta XT and it wants no high up
let me show you what this looks like
Russell also the blow pop full pipe and
as you can see here where we’re getting
a buffer of bytes and that is not quite
what we want we expect that this to be
the contents of the data of txt file and
that is yes because in in programming
and in the computer strings are used to
long set of lines it doesn’t know how to
interpret that in text unless it has
some kind of mapping to an encoding
table a character encoding the most
common character encoding is utf-8 let’s
run that again yes we have let’s start
by I don’t know splitting this into an
array so split is just a method on the
string object that splits the string
into an array by splitting it using this
character here and this is a line break
so if we run this we’re gonna see an
array of straights
it’s an extra line here I it’s because
files always tend to have one final line
break so we get rid of that by just
calling trim on the string before we
pass it into split and what trim does is
that it just removes any line breaks or
space it at the end and star on a string
if you run that that little string at
the end is now gone before we start
using reduce on these lines
I would like to convert them into a more
manageable object first using map I’m
every line and I’m gonna split it on tab
characters see what that looks like okay
cool now we have an array of arrays
where each array is basically the
equivalent this let’s reduce it remember
that reduce takes two arguments first
takes a function and it also takes a
starting object and in the last episode
we used a number as starting object like
this but in this case we are going to
create an object clip so we’re going to
pass it object the function that we pass
to reduce once two arguments the first
one is the object that we are
constructing the the end goal that we
talked about in the beginning of this
episode and it’s it’s this one and it’s
going to be passed here on the first
loop and the second argument is the
thing that we are iterating in this case
it’s going to be the line and my what I
mean by that is these so reduce is going
to receive this item on the path this
array on the first iteration it will
receive this array on the second
iteration and so on let’s run that so
far
whoops ads returning undefined and that
is because output will be whatever
reduce returns on its final iteration so
let’s return the customer object and
alright it’s an empty object that is
because we’re returning it here and it’s
empty because we’re not doing anything
with it yet just for kicks let me
console.log the line out on it BAM
so you’ll see here that reduce iterates
over the array of arrays that this map
function trades so for each iteration it
receives an array mother array that is
the equivalent of lines in data dot txt
let’s get rid of this console.log i
wanna rename this customers as we’re
making a customer’s object and for every
customer we’re gonna make a property
remember that the first item of the line
first part is the name we’re gonna make
that an empty array let’s run it okay
cool we have an empty array for Mark
Johnson and we have an empty ready for
Nikita Smith and this is because even
though it will get this line than this
line then this line it will simply
overwrite the Mark Jones and property
every time and the Nikita sliprock every
time and now we’re gonna hand the
ordered items so we take this of it and
push to it we push an object so the one
name that is the second part of the line
that is the third part of the line and
we want the quantity which is the 4.5
line and we run that oh that’s a bit
hard to read I’m gonna teach you a trick
now check this out
Jason dot string a fie no to run that
again
Oh much better
so what we did here was create a JSON
string from the the output with two
spaces for indentation we have a bug
because only the last item here and the
caught here is actually being being
added to the array and that is because
we are overriding it here so we have to
copy this one
and just make sure that now we are
reusing the existing array if there
exists one otherwise we’re signing
anyway and we have an output so waffle
iron blender both there’s no quantity oh
I have a bug time free getting tired
right alright and we are done today we
looked at a more advanced reduce example
where instead of using a number we used
eight an object literal we also see some
chaining going on here
good functional code is made up of small
functions that do one thing and you just
find them all together and that is what
we do here we have a trim with a split
we have a map which in turn uses split
inside of it ah and we have a reduce the
chain ability that you see here is
something that you’re gonna see a lot of
if you do functional program I am going
to nibble a bit on the jura superstition
whiskey that we are supposed to spring
on the canoe trip the the other guys
won’t know that enabled because this
I’ll tear them so I am on vacation next
week so there won’t be an episode next
Monday but there will be the Monday
after that so please tell me what you
think that that episode should be about
either comment down below or send me a
tweet at MV Jamie oh and two weeks
without an episode that’s a long time
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of you guys this is good morning
and for me this is good night until next time stay curious