# About Testing Float32 values for equality

**URL:** <https://discourse.julialang.org/t/about-testing-float32-values-for-equality/22221>\
**Category:** New to Julia\
**Created:** [March 22, 2019, 10:13pm UTC](https://discourse.julialang.org/t/about-testing-float32-values-for-equality/22221 "2019-03-22T22:13:39Z")\
**Posts on this page:** 10\
**Page:** 1

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**Author:** ![samq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/samq/32/47935_2.png) [@samq](https://discourse.julialang.org/u/samq)\
**Post date:** [March 22, 2019, 10:13pm UTC](https://discourse.julialang.org/t/about-testing-float32-values-for-equality/22221/1 "2019-03-22T22:13:40Z")

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I’m searching for a floating point value in an array.  
I already know that index 231 has the Float32 value of 0.011764707.

When I test for equality in the code below it fails the test.  
Why are these values; Float32(value) and 0.011764707 not equal?  
Am I testing wrongly?

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**Author:** ![yuyichao](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yuyichao/32/20_2.png) [@yuyichao](https://discourse.julialang.org/u/yuyichao)\
**Post date:** [March 22, 2019, 10:25pm UTC](https://discourse.julialang.org/t/about-testing-float32-values-for-equality/22221/2 "2019-03-22T22:25:57Z")

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Most likely because

> [@samq](#):
>
> 0.011764707

Is not a Float64. Since this number is most likely not exactly representable by binary floating point (disclaimer, I didn’t check that) it’s closest approximation, I.e. the parsing result will be different for the two types even though the printing are the same. If you use a float32 literal (add a f0 at the end) the condition should be true assuming what you said is indeed the output of your program.

P.s. when you paste code you should make it either runnable or at least show the result you are confused about. The code you paste right now is no more than some random code that may or may not support what your question.

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**Author:** ![simonbyrne](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/simonbyrne/32/19_2.png) [@simonbyrne](https://discourse.julialang.org/u/simonbyrne)\
**Post date:** [March 22, 2019, 10:35pm UTC](https://discourse.julialang.org/t/about-testing-float32-values-for-equality/22221/3 "2019-03-22T22:35:56Z")

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`0.011764707` is a `Float64` literal: it will give you the `Float64` closest to 0.011764707, which is exactly

```julia
julia> using Printf

julia> @printf "%.60f" 0.011764707
0.011764706999999999248451842959184432402253150939941406250000

```

You want `0.011764707f0` which is a `Float32` literal, which has a slightly different value:

```julia
julia> @printf "%.60f" 0.011764707f0
0.011764707043766975402832031250000000000000000000000000000000

```

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<div class="post-metadata">

**Author:** ![samq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/samq/32/47935_2.png) [@samq](https://discourse.julialang.org/u/samq)\
**Post date:** [March 23, 2019, 3:22am UTC](https://discourse.julialang.org/t/about-testing-float32-values-for-equality/22221/4 "2019-03-23T03:22:07Z")

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I did what both @yuyichao and @simonbyrne suggested and it still didn’t work properly. Here is a more complete, runnable version of the code:

```julia
using Flux, Flux.Data.MNIST, Statistics
using Flux: onehotbatch, onecold, crossentropy, throttle
using Base.Iterators: repeated, partition
using Printf, BSON

train_labels = MNIST.labels() # 60,000
train_imgs = MNIST.images() # 60,000

function make_minibatch(X, Y, idxs)  
    X_batch = Array{Float32}(undef, size(X[1])..., 1, length(idxs))
      # Creates X-batch and the associated Y_Batch of labels
     for i in 1:length(idxs) # This line loops from 1 to 128 (or whatever the lebgth of the iterator partition)
         X_batch[:, :, :, i] = Float32.(X[idxs[i]]) # uses idxs iterator to place X[1 to 128] in Xbatch[28, 28, 1, (1 to 128)]
     end
     Y_batch = onehotbatch(Y[idxs], 0:9) # provides an efficient way of accessing labels

     return (X_batch, Y_batch)
end

batch_size = 128
mb_idxs = partition(1:length(train_imgs), batch_size) # divides 60,000 into partitions or batches of 128

train_set = [make_minibatch(train_imgs, train_labels, i) for i in mb_idxs]
a = train_set[1,1]

value = (a[1])[231]
searchvalue = 0.011764707f0
println("typeof(value) = ", typeof(value))
println("typeof(searchvalue) = ", typeof(searchvalue))
println("for ", 231, " in a[1] = ", value)

if value == searchvalue
  println("FOUND IT!!!")
else
  println("Failed to locate it")
end

```

Here is the output:  
typeof(value) = Float32  
typeof(searchvalue) = Float32  
for 231 in a[1] = 0.11764707  
Failed to locate it

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<div class="post-metadata">

**Author:** ![yuyichao](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yuyichao/32/20_2.png) [@yuyichao](https://discourse.julialang.org/u/yuyichao)\
**Post date:** [March 23, 2019, 3:30am UTC](https://discourse.julialang.org/t/about-testing-float32-values-for-equality/22221/5 "2019-03-23T03:30:19Z")

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> [@samq](#):
>
> searchvalue = 0.011764707f0

> [@samq](#):
>
> for 231 in a[1] = 0.11764707

You realized that the two numbers aren’t the same do you?

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<div class="post-metadata">

**Author:** ![samq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/samq/32/47935_2.png) [@samq](https://discourse.julialang.org/u/samq)\
**Post date:** [March 23, 2019, 3:34am UTC](https://discourse.julialang.org/t/about-testing-float32-values-for-equality/22221/6 "2019-03-23T03:34:45Z")

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@yuyichao  
Yes, but I understood the 0.11764707f0 Float32 literal would be the same as 0.11764707 Float32 value, because the straight up 0.11764707 != 0.11764707…hence the problem…

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<div class="post-metadata">

**Author:** ![yuyichao](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yuyichao/32/20_2.png) [@yuyichao](https://discourse.julialang.org/u/yuyichao)\
**Post date:** [March 23, 2019, 3:35am UTC](https://discourse.julialang.org/t/about-testing-float32-values-for-equality/22221/7 "2019-03-23T03:35:40Z")

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No, assuming you didn’t have a typo in your code, did you realized that one of them was `0.0117....` while the other one is `0.117....`?

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<div class="post-metadata">

**Author:** ![samq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/samq/32/47935_2.png) [@samq](https://discourse.julialang.org/u/samq)\
**Post date:** [March 23, 2019, 3:38am UTC](https://discourse.julialang.org/t/about-testing-float32-values-for-equality/22221/8 "2019-03-23T03:38:40Z")

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@yuyichao  
OMG!!!

I am truly a complete idiot and hope you accept my apology for wasting your time!

I will make a strong effort not to do this again.

Thank you sir, for your help.

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<div class="post-metadata">

**Author:** ![yuyichao](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yuyichao/32/20_2.png) [@yuyichao](https://discourse.julialang.org/u/yuyichao)\
**Post date:** [March 23, 2019, 3:39am UTC](https://discourse.julialang.org/t/about-testing-float32-values-for-equality/22221/9 "2019-03-23T03:39:38Z")

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The issue about Float32 vs Float64 still apply so most of the time/effort was not wasted…

And just to note that this is why I asked for either the full code or the output… to confirm your claim…

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<div class="post-metadata">

**Author:** ![samq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/samq/32/47935_2.png) [@samq](https://discourse.julialang.org/u/samq)\
**Post date:** [March 23, 2019, 3:41am UTC](https://discourse.julialang.org/t/about-testing-float32-values-for-equality/22221/10 "2019-03-23T03:41:17Z")

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@yuyichao  
Thank you for the “full runnable code” idea; it made all the difference.

Thanks again.