Truncate a float in Erlang

Question

I am using a function to create a list from a float.

 float_to_list(0.02).

It returns:

"2.00000000000000000000e-002"

I need it to give me a number exactly like:

"0.20"

If I fed it 5.23

"5.23"

If I fed it 5.5

"5.50"

So basically the number rounded to two decimal places. Probably an easy fix.

Thanks

EDIT:

I would like to use the io format it looks like it might work,

but it dosen't in this example:

wxTextCtrl:setValue( TcGrossProfit, io:format("~p", [NUMBER]), ),

seems textctrl wants a string, I don't want to print it to the screen.

Solution 1

Are you looking for something like this:

6> F = 5/2.
2.50000
7> io_lib:format("~.1f",[F]).
["2.5"]
8> io_lib:format("~.2f",[F]).
["2.50"]
9> io_lib:format("~.3f",[F]).
["2.500"]

If yes, have a look at the io_lib module.

Solution 2

mochinum:digits converts a float to a string with an appropriate level of precision.

1> mochinum:digits(1.1).
"1.1"
2> mochinum:digits(1.2345).
"1.2345"

Not exactly what the OP requested, but useful nonetheless.

Solution 3

Alternatively you could use the function you were already using.

float_to_list(0.02,[{decimals, 2}]) outputs '0.02'

Or for Elixir users ;)

:erlang.float_to_list(5.231,[{:decimals, 2}]) outputs '5.2'

Solution 4

This link provides functions that truncate/floor or ceil or round a float. Given those you can round to 2 digits by multiplying by 100, rounging and then dividing back by 100 (and possibly rounding again to avoid precision errors)

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Comments

[ndim]

+1 for being the only answer mentioning io_lib - the thing that formats to strings (aka lists), instead of just printing the output like io.

[ndim]

@pst Still, the only answer mentioning io_lib, as of now.