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ITunes review URL and iOS 7 (ask user to rate our app) AppStore show a blank page
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Ruby optional parameters
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This isn't possible with ruby currently. You can't pass 'empty' attributes to methods. The cl...
Changing iframe src with Javascript
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In this case, it's probably because you are using the wrong brackets here:
document.getElemen...
Why does Bootstrap set the line-height property to 1.428571429?
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Uncaught TypeError: Cannot read property 'msie' of undefined - jQuery tools
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How do I echo and send console output to a file in a bat script?
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How to update a value, given a key in a hashmap?
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How can I pass a list as a command-line argument with argparse?
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dplyr summarise: Equivalent of “.drop=FALSE” to keep groups with zero length in output
...e .drop argument that does just what you asked for:
df = data.frame(a=rep(1:3,4), b=rep(1:2,6))
df$b = factor(df$b, levels=1:3)
df %>%
group_by(b, .drop=FALSE) %>%
summarise(count_a=length(a))
#> # A tibble: 3 x 2
#> b count_a
#> <fct> <int>
#> 1 1 ...