# I do not understand this error: MethodError: no method matching iterate(::DataFrame)

**URL:** <https://discourse.julialang.org/t/i-do-not-understand-this-error-methoderror-no-method-matching-iterate-dataframe/34530>\
**Category:** General Usage\
**Tags:** first-steps\
**Created:** [February 12, 2020, 5:10pm UTC](https://discourse.julialang.org/t/i-do-not-understand-this-error-methoderror-no-method-matching-iterate-dataframe/34530 "2020-02-12T17:10:16Z")\
**Posts on this page:** 1\
**Showing post:** 4

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**Author:** ![nilshg](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nilshg/32/2283_2.png) [@nilshg](https://discourse.julialang.org/u/nilshg)\
**Post date:** [February 12, 2020, 5:34pm UTC](https://discourse.julialang.org/t/i-do-not-understand-this-error-methoderror-no-method-matching-iterate-dataframe/34530/4 "2020-02-12T17:34:30Z")

</div>

Your example is not an MWE (see [Please read: make it easier to help you](https://discourse.julialang.org/t/psa-make-it-easier-to-help-you/14757)), but it looks like you’re calling `compose(c, ...)` in your loop without first defining `c`.

It might be useful to have a look at the Julia language docs and maybe the documentation for the packages you’re using to get the hang of the basic usage, as step-by-step debugging via Discourse might be pretty time consuming…

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