Problems with printing a table

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#1

Hello everyone, I would like to know what is wrong with my code, I am learning and I would like to print my table in these two ways, how is this possible?

students = {
    {name = "Miles Davis", instrument = "trumpet"},
    {name= "John Coltrane", instrument = "saxophone"},
    {name= "Bill Evans", instrument = "piano"},
    {name= "Wynton Kelly", instrument = "piano"}
}

-- Way 1 to print
for k, v in pairs(students) do
	print(k, v)
end

-- Way 2 to print
print(students[name][instrument])

I have these two ways to print, it is part of my learning

#2

What do you want the output to look like?

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#3 
for k, v in ipairs(students) do
	print(v.name, v.instrument) -- "v" is the table 
end
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#4

same like this one:
print(v.name, v.instrument) – “v” is the table

#5

How could i do same output in this print?
print(students[name][instrument])

#6

From your code it looks like you want to be formatting your table like this

students = {
    ["Miles Davis"] = {instrument = "trumpet"},
    ["John Coltrane"] = {instrument = "saxophone"},
    ["Bill Evans"] = {instrument = "piano"},
    ["Wynton Kelly"] = {instrument = "piano"}
}
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#7

I don’t really understand what you’re asking, sorry.

#8

And how could i do the output with a print for this?
example
print(students[1][instruments]) → or am i wrong?¿

#9

You would do

print(students['Miles Davis'], students['John Coltrane']) -- etc
#10

That would be the old way, you would do

print(students["Miles Davis"]["instrument"])

^ this would print Miles Davis’s instrument.

1 Like
#11

Oh I see, thank you all very much indeed!! :smiley: :smiley:

#12

If you just want the name and the instrument do:

students = {
   ["Miles Davis"] = "trumpet",
   ["John Coltrane"] = "saxaphone"
}

for k, v in pairs (students) do
   print(k, v)
end

This will give you in the output:
Miles Davis trumpet
John Coltrane saxaphone

you can do this if you want to add a colon or equal sign:

print (k .. ": " .. v)

Ouput:
Miles Davis: trumpet
John Coltrane: saxophone

Hope this is what you want, you should add what you want your output to be. :slight_smile:

2 Likes
#13

You are currently using arrays, which contain dictionaries. What is the difference between a dictionary and an array?

Array

local fruits = {"apples", "passion fruit", "strawberries"}

print(fruits[1]) --> apples
print(fruits[2]) --> passion fruit
print(fruits["apples"]) --> nil
print(fruits[apples]) --> nil

Tables have indexes (keys) and elements. A key sort of represents the position in that table. If index of an array is equal to 1, apples will be printed.

Why doesn’t the last two examples work? Because There is no “apples” index, so the table returns nil.
Strings need to be wrapped in brackets, so the last example results in nil as well, because apples doesn’t exist. You can, however, write the following:

local fruits = {"apples", "passion fruit", "strawberries"}

local apples = "apples"
print(fruits[apples]) -->> nil, there is no apples index

Dictionary

As opposed to tables, dictionaries have different indexes. They are named that way because their structure is dictionary-like.

local cars = {
	["BMW"] = "black";
	["Lexus"] = "blue";
	["Ferrari"] = "red";
}

print(cars["BMW"]) -->> black
print(cars[1]) --> nil
print(cars[Ferrari]) --> nil

Indexes are strings, but they can be numbers as well. There is no index 1 in this dictionary, so it prints nil. The last option returns nil too again, because Ferrari (not a string, but a variable) is not defined.
You could do the same as above:

local Ferrari = "Ferrari"
print(cars[Ferrari]) --> red

Dictionaries can also have numbers as indexes:

local cars = {
	[10] = "black";
	[100] = "blue";
	[1000] = "red";
}

print(cars[1000]) -->> red

Your examples

students = {
	{name = "Miles Davis", instrument = "trumpet"},
	{name= "John Coltrane", instrument = "saxophone"},
	{name= "Bill Evans", instrument = "piano"},
	{name= "Wynton Kelly", instrument = "piano"}
}

for i, v in pairs(students) do
	print(i, v)
end

-- OUTPUT:
-->> 1 {...} --> because elements are arrays
-->> ... and so on ...

for i, array in pairs(students) do
	print(array["name"], array["instrument"])
end

-- OUTPUT:
-->> Miles Davis trumpet
-->> ... and so on ...

What about the second option?

print(students[1]["name"], students[1]["instrument"])

-- OUTPUT
-->> Miles Davis trumpet

--[[
	table: STUDENTS
	index: 1
	element with index: ARRAY
	array[1]: nil --> no index one in that aray
	array["name"]: Miles Davis
	array["instrument"]: trumpet
]]

Hopefully you find this post useful. I will update it a little bit later.

2 Likes
#14

Wow! Thank you very much for this great explanation, I really did not expect it, thank you friend!

1 Like